Document translation script

docs/translating-guide.md

@@ -14,5 +14,13 @@ That's it! When MetaMask is loaded on a computer with that language set as the s
 
 ## Testing
 
-To verify that your translation works, you will need to [build a local copy](https://github.com/MetaMask/metamask-extension#building-locally) of MetaMask.
+To automatically see if you are missing any phrases to translate, we have a script you can run (if you know how to use the command line). The script is:
+
+```
+node development/verify-locale-strings.js $YOUR_LOCALE
+```
+
+Where `$YOUR_LOCALE` is your [locale string](https://r12a.github.io/app-subtags/), i.e. the name of your language folder.
+
+To verify that your translation works in the app, you will need to [build a local copy](https://github.com/MetaMask/metamask-extension#building-locally) of MetaMask. You will need to change your browser language, your operating system language, and restart your browser (sorry it's so much work!).