Add `flake8-fixme` documentation (#5868)

## Summary

Completes documentation for the `flake8-fixme` (`FIX`) ruleset. Related
to #2646.

Tweaks the violation message. For example,

```
FIX001 Line contains FIXME
```

becomes

```
FIX001 Line contains FIXME, consider resolving the issue
```

This is because the previous message was unclear if it was warning
against the use of FIXME tags per se, or the code the FIXME tag was
annotating.


## Test Plan

`cargo test && python scripts/check_docs_formatted.py`

crates/ruff/src/rules/flake8_fixme/rules/todos.rs

@@ -3,39 +3,114 @@ use ruff_macros::{derive_message_formats, violation};
 
 use crate::directives::{TodoComment, TodoDirectiveKind};
 
+/// ## What it does
+/// Checks for "TODO" comments.
+///
+/// ## Why is this bad?
+/// "TODO" comments are used to describe an issue that should be resolved
+/// (usually, a missing feature, optimization, or refactoring opportunity).
+///
+/// Consider resolving the issue before deploying the code.
+///
+/// Note that if you use "TODO" comments as a form of documentation (e.g.,
+/// to [provide context for future work](https://gist.github.com/dmnd/ed5d8ef8de2e4cfea174bd5dafcda382)),
+/// this rule may not be appropriate for your project.
+///
+/// ## Example
+/// ```python
+/// def greet(name):
+///     return f"Hello, {name}!"  # TODO: Add support for custom greetings.
+/// ```
 #[violation]
 pub struct LineContainsTodo;
 impl Violation for LineContainsTodo {
     #[derive_message_formats]
     fn message(&self) -> String {
-        format!("Line contains TODO")
+        format!("Line contains TODO, consider resolving the issue")
     }
 }
 
+/// ## What it does
+/// Checks for "FIXME" comments.
+///
+/// ## Why is this bad?
+/// "FIXME" comments are used to describe an issue that should be resolved
+/// (usually, a bug or unexpected behavior).
+///
+/// Consider resolving the issue before deploying the code.
+///
+/// Note that if you use "FIXME" comments as a form of documentation, this
+/// rule may not be appropriate for your project.
+///
+/// ## Example
+/// ```python
+/// def speed(distance, time):
+///     return distance / time  # FIXME: Raises ZeroDivisionError for time = 0.
+/// ```
 #[violation]
 pub struct LineContainsFixme;
 impl Violation for LineContainsFixme {
     #[derive_message_formats]
     fn message(&self) -> String {
-        format!("Line contains FIXME")
+        format!("Line contains FIXME, consider resolving the issue")
     }
 }
 
+/// ## What it does
+/// Checks for "XXX" comments.
+///
+/// ## Why is this bad?
+/// "XXX" comments are used to describe an issue that should be resolved.
+///
+/// Consider resolving the issue before deploying the code, or, at minimum,
+/// using a more descriptive comment tag (e.g, "TODO").
+///
+/// ## Example
+/// ```python
+/// def speed(distance, time):
+///     return distance / time  # XXX: Raises ZeroDivisionError for time = 0.
+/// ```
 #[violation]
 pub struct LineContainsXxx;
 impl Violation for LineContainsXxx {
     #[derive_message_formats]
     fn message(&self) -> String {
-        format!("Line contains XXX")
+        format!("Line contains XXX, consider resolving the issue")
     }
 }
 
+/// ## What it does
+/// Checks for "HACK" comments.
+///
+/// ## Why is this bad?
+/// "HACK" comments are used to describe an issue that should be resolved
+/// (usually, a suboptimal solution or temporary workaround).
+///
+/// Consider resolving the issue before deploying the code.
+///
+/// Note that if you use "TODO" comments as a form of documentation, this
+/// rule may not be appropriate for your project.
+///
+/// ## Example
+/// ```python
+/// import os
+///
+///
+/// def running_windows():  # HACK: Use platform module instead.
+///     try:
+///         os.mkdir("C:\\Windows\\System32\\")
+///     except FileExistsError:
+///         return True
+///     else:
+///         os.rmdir("C:\\Windows\\System32\\")
+///         return False
+/// ```
 #[violation]
 pub struct LineContainsHack;
 impl Violation for LineContainsHack {
     #[derive_message_formats]
     fn message(&self) -> String {
-        format!("Line contains HACK")
+        format!("Line contains HACK, consider resolving the issue")
     }
 }
 

crates/ruff/src/rules/flake8_fixme/snapshots/ruff__rules__flake8_fixme__tests__line-contains-fixme_T00.py.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/ruff/src/rules/flake8_fixme/mod.rs
 ---
-T00.py:7:3: FIX001 Line contains FIXME
+T00.py:7:3: FIX001 Line contains FIXME, consider resolving the issue
   |
 5 | # HACK: hack
 6 | # hack: hack
@@ -10,7 +10,7 @@ T00.py:7:3: FIX001 Line contains FIXME
 8 | # fixme: fixme
   |
 
-T00.py:8:3: FIX001 Line contains FIXME
+T00.py:8:3: FIX001 Line contains FIXME, consider resolving the issue
   |
 6 | # hack: hack
 7 | # FIXME: fixme

crates/ruff/src/rules/flake8_fixme/snapshots/ruff__rules__flake8_fixme__tests__line-contains-hack_T00.py.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/ruff/src/rules/flake8_fixme/mod.rs
 ---
-T00.py:5:3: FIX004 Line contains HACK
+T00.py:5:3: FIX004 Line contains HACK, consider resolving the issue
   |
 3 | # XXX: xxx
 4 | # xxx: xxx
@@ -11,7 +11,7 @@ T00.py:5:3: FIX004 Line contains HACK
 7 | # FIXME: fixme
   |
 
-T00.py:6:3: FIX004 Line contains HACK
+T00.py:6:3: FIX004 Line contains HACK, consider resolving the issue
   |
 4 | # xxx: xxx
 5 | # HACK: hack

crates/ruff/src/rules/flake8_fixme/snapshots/ruff__rules__flake8_fixme__tests__line-contains-todo_T00.py.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/ruff/src/rules/flake8_fixme/mod.rs
 ---
-T00.py:1:3: FIX002 Line contains TODO
+T00.py:1:3: FIX002 Line contains TODO, consider resolving the issue
   |
 1 | # TODO: todo
   |   ^^^^ FIX002
@@ -9,7 +9,7 @@ T00.py:1:3: FIX002 Line contains TODO
 3 | # XXX: xxx
   |
 
-T00.py:2:3: FIX002 Line contains TODO
+T00.py:2:3: FIX002 Line contains TODO, consider resolving the issue
   |
 1 | # TODO: todo
 2 | # todo: todo

crates/ruff/src/rules/flake8_fixme/snapshots/ruff__rules__flake8_fixme__tests__line-contains-xxx_T00.py.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/ruff/src/rules/flake8_fixme/mod.rs
 ---
-T00.py:3:3: FIX003 Line contains XXX
+T00.py:3:3: FIX003 Line contains XXX, consider resolving the issue
   |
 1 | # TODO: todo
 2 | # todo: todo
@@ -11,7 +11,7 @@ T00.py:3:3: FIX003 Line contains XXX
 5 | # HACK: hack
   |
 
-T00.py:4:3: FIX003 Line contains XXX
+T00.py:4:3: FIX003 Line contains XXX, consider resolving the issue
   |
 2 | # todo: todo
 3 | # XXX: xxx