Create per-rule pages and link from README (#2644)

crates/ruff_dev/src/generate_docs.rs

@@ -1 +1,32 @@
+//! Generate Markdown documentation for applicable rules.
+#![allow(clippy::print_stdout, clippy::print_stderr)]
 
+use std::fs;
+
+use anyhow::Result;
+use strum::IntoEnumIterator;
+
+use ruff::registry::Rule;
+
+#[derive(clap::Args)]
+pub struct Args {
+    /// Write the generated docs to stdout (rather than to the filesystem).
+    #[arg(long)]
+    pub(crate) dry_run: bool,
+}
+
+pub fn main(args: &Args) -> Result<()> {
+    for rule in Rule::iter() {
+        if let Some(explanation) = rule.explanation() {
+            let explanation = format!("# {} ({})\n\n{}", rule.as_ref(), rule.code(), explanation);
+
+            if args.dry_run {
+                println!("{}", explanation);
+            } else {
+                fs::create_dir_all("docs/rules")?;
+                fs::write(format!("docs/rules/{}.md", rule.as_ref()), explanation)?;
+            }
+        }
+    }
+    Ok(())
+}