Missing updated auth configuration instructions in the README

[vgeorge]

After we merged #339 the instructions for configuring the auth became outdated. This is critical as running the app without this is not possible. Cypress and API tests were not affected.

cc @kamicut @batpad

[vgeorge]

How to replicate this:

• Clear .env.local file
• Visit https://mapping.team
• Create a new client with callback URL http://127.0.0.1:3000/api/auth/callback/osm-teams
• Add client id and secret to .env.local file:

OSM_TEAMS_CLIENT_ID=<client id>
OSM_TEAMS_CLIENT_SECRET=<client secret>

• Start the app locally with yarn dev and try signing in
• The following error should appear:

I was able to inspect browser redirection and the following request is returning 500 status:

https://auth.mapping.team/hyauth/oauth2/auth?client_id=ff68f1bc-6e99-4db2-9e1c-ada5a5cdc7f7&scope=openid%20offline&response_type=code&redirect_uri=http%3A%2F%2F127.0.0.1%3A3000%2Fapi%2Fauth%2Fcallback%2Fosm-teams&state=redacted-state

I tried to log in with other credentials (client id/secret) provided by Marc Farra and it worked, so my guess here is that the callback URL should be different.