docs: add link to ripgrep docs for including/excluding files

README.md

@@ -153,6 +153,13 @@ few things you can do to improve performance:
 - Set the `debug = true` option, which will log debug information to your
   `:messages` in Neovim. You can copy paste these commands to your terminal and
   try to figure out why the search is slow.
+- Use ripgrep's extensive options to exclude/include files
+  ([ripgrep docs](https://github.com/BurntSushi/ripgrep/blob/master/GUIDE.md#automatic-filtering))
+
+  - ripgrep supports global as well project/directory specific ignore files. By
+    default, it uses `.gitignore`, `.git/info/exclude`, `.ignore`, and
+    `.rgignore` files.
+
 - If you still experience performance issues, please open an issue for
   discussion.