doc: add documentation for TRY002 (#2655)

docs/rules/raise-vanilla-class.md

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+# raise-vanilla-class (TRY002)
+
+Derived from the **tryceratops** linter.
+
+### What it does
+Checks for code that raises `Exception` directly.
+
+### Why is this bad?
+Handling such exceptions requires the use of `except Exception`, which
+captures _any_ raised exception, including failed assertions,
+division by zero, and more.
+
+Prefer to raise your own exception, or a more specific built-in
+exception, so that you can avoid over-capturing exceptions that you
+don't intend to handle.
+
+### Example
+```py
+def main_function():
+    if not cond:
+        raise Exception()
+def consumer_func():
+    try:
+        do_step()
+        prepare()
+        main_function()
+    except Exception:
+        logger.error("Oops")
+```
+
+Use instead:
+```py
+def main_function():
+    if not cond:
+        raise CustomException()
+def consumer_func():
+    try:
+        do_step()
+        prepare()
+        main_function()
+    except CustomException:
+        logger.error("Main function failed")
+    except Exception:
+        logger.error("Oops")

docs/rules/raise_vanilla_class.md

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+# raise-vanilla-class (TRY002)
+Derived from the **tryceratops** linter.
+
+### What it does
+Checks for bare exceptions.
+
+## Why is this bad?
+It's hard to capture generic exceptions making it hard for handling specific scenarios.
+
+## Example
+```py
+def main_function():
+    if not cond:
+        raise Exception()
+def consumer_func():
+    try:
+        do_step()
+         prepare()
+        main_function()
+    except Exception:
+        logger.error("I have no idea what went wrong!!")
+```
+
+## How it should be
+```py
+def main_function():
+    if not cond:
+        raise CustomException()
+def consumer_func():
+    try:
+        do_step()
+        prepare()
+        main_function()
+    except CustomException:
+        logger.error("Main function failed")
+    except Exception:
+        logger.error("I have no idea what went wrong!!")
+```