docs: fix Deno setup without package.json (#4896)

* docs: fix Deno setup without package.json

* docs: clarify Deno 2 requirement

Author: awnoa

docs/guides/getting-started.md

@@ -24,6 +24,8 @@ bun add -d @commitlint/cli @commitlint/config-conventional
 
 ```sh [deno]
 deno add -D npm:@commitlint/cli npm:@commitlint/config-conventional
+# Deno 2 only: create a local node_modules directory for Node.js module resolution
+deno install --node-modules-dir=auto
 ```
 
 :::