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_rules_table.rs

@@ -1,4 +1,6 @@
 //! Generate a Markdown-compatible table of supported lint rules.
+//!
+//! Used for <https://beta.ruff.rs/docs/rules/>.
 
 use itertools::Itertools;
 use strum::IntoEnumIterator;