Document --debug-transforms

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Crawl uploaded exercise solutions
 - Explain what PFERD is doing and why (`--explain`)
 - More control over output (`--status`, `--report`)
+- Debug transform rules with `--debug-transforms`
 - Print report after exiting via Ctrl+C
 - Store crawler reports in `.report` JSON file
 - Extensive config file documentation (`CONFIG.md`)

CONFIG.md

@@ -205,6 +205,9 @@ They are specified line-by-line in a crawler's `transform` option. When a
 crawler needs to apply a rule to a path, it goes through this list top-to-bottom
 and choose the first matching rule.
 
+To see this process in action, you can use the `--debug-transforms` or flag or
+the `--explain` flag.
+
 Each line has the format `SOURCE ARROW TARGET` where `TARGET` is optional.
 `SOURCE` is either a normal path without spaces (e. g. `foo/bar`), or a string
 literal delimited by `"` or `'` (e. g. `"foo\" bar/baz"`). Python's string