doc(readme): add auth.error check to auto sign in

[jnschbrt]

• add auth.error to auto login to prevent infinite loop when request fails

I had this problem when I got a CORS error. Therefore an endless loop was triggered during auto login

Checklist

• [ ] This PR makes changes to the public API
• [ ] I have included links for closing relevant issue numbers

[pamapa]

Thanks for reporting back and improving the docs.

I thought hasTriedSignin would take care of endless loops, maybe we just need to flip the sequence?

  auth.signinRedirect();
  setHasTriedSignin(true);

->
  setHasTriedSignin(true);
  auth.signinRedirect();