Add script to report progress with matching

docs/retail_versions.md

@@ -115,6 +115,12 @@ void foo() {
 
 ## Diff Tools
 
+### retail_progress.py
+
+Running `./retail_progress.py file.c` will attempt to figure out which functions
+in a file still need to match for `gc-eu-mq`. To get an overview of diffs for
+all files, run `./retail_progress.py` with no arguments.
+
 ### asm-differ / diff.py
 
 To diff assembly for a single function in `gc-eu-mq`, run e.g.