duplicate imports in the doc() documentation

[davie-robertson]

https://github.com/FirebaseExtended/rxfire/blob/main/docs/firestore.md#doc

doc is being imported from both rxfire and firebase so code won't run

  import { **doc** } from 'rxfire/firestore';
  import { initializeApp } from 'firebase/app';
  import { getFirestore, **doc**, setDoc } from 'firebase/firestore';

[julienreszka]

Did you mitigate this if so how did you do it?

[davideast]

Right now we recommend using the as syntax to rewrite an import. We'll revisit the API in the next release to avoid collisions.

 import { doc as doc$ } from 'rxfire/firestore';
 import { initializeApp } from 'firebase/app';
 import { getFirestore, **doc**, setDoc } from 'firebase/firestore';