Merge pull request #957 from spotify/add-auth-backend-docs

Add required env vars for backends in README

plugins/auth-backend/README.md

@@ -7,6 +7,18 @@ This is the backend part of the auth plugin.
 It responds to auth requests from the frontend, and fulfills them by delegating
 to the appropriate provider in the backend.
 
+## Requirements
+
+Needs AUTH_GOOGLE_CLIENT_ID and AUTH_GOOGLE_CLIENT_SECRET set in the environment for the backend to startup
+
+## Local development
+
+export AUTH_GOOGLE_CLIENT_ID=<INSERT_CLIENT_ID_HERE>
+read -r AUTH_GOOGLE_CLIENT_SECRET
+<COPY_PASTE_CLIENT_SECRET_HERE>
+export AUTH_GOOGLE_CLIENT_SECRET
+run `yarn start` in packages/backend folder
+
 ## Links
 
 - (The Backstage homepage)[https://backstage.io]