Document ruff_dev and format_dev (#5648)

## Summary

Document all `ruff_dev` subcommands and document the `format_dev` flags
in the formatter readme.

CC @zanieb please flag everything that isn't clear or missing

## Test Plan

n/a

crates/ruff_dev/src/generate_all.rs

@@ -21,7 +21,7 @@ pub(crate) enum Mode {
     /// Don't write to the file, check if the file is up-to-date and error if not.
     Check,
 
-    /// Write the generated help to stdout (rather than to `docs/configuration.md`).
+    /// Write the generated help to stdout.
     DryRun,
 }