chmod recursively to satisfy zsh "insecure directories" warning

without `-R` only `share` is updated, leaving `share/zsh/site-functions` unchanged, so the warning won't go away

docs/Shell-Completion.md

@@ -52,7 +52,7 @@ You may also need to forcibly rebuild `zcompdump`:
 Additionally, if you receive "zsh compinit: insecure directories" warnings when attempting to load these completions, you may need to run this:
 
 ```sh
-  chmod go-w "$(brew --prefix)/share"
+  chmod -R go-w "$(brew --prefix)/share"
 ```
 
 ## Configuring Completions in `fish`