docs: add config example for pnpm (#1400)

* Add config example for pnpm 

While using `pnpm` as package manger `transformIgnorePatterns` should refernce to package inside `.pnpm` folder.
[source](https://jestjs.io/docs/configuration#transformignorepatterns-arraystring)

* Update website/docs/ReactNavigation.md

---------

Co-authored-by: Maciej Jastrzebski <mdjastrzebski@gmail.com>

Author: yjose

website/docs/ReactNavigation.md

@@ -140,6 +140,9 @@ module.exports = {
   setupFiles: ['./node_modules/react-native-gesture-handler/jestSetup.js'],
   transformIgnorePatterns: [
     'node_modules/(?!(jest-)?@?react-native|@react-native-community|@react-navigation)',
+
+    // For pnpm you need to use inlcude `(?!(?:.pnpm/)?` part like this:
+    // 'node_modules/(?!(?:.pnpm/)?((jest-)?@?react-native|@react-native-community|@react-navigation))',
   ],
 };
 ```