Update Docs on Background Indexing

Moved from GitHub dgraph/5568

Posted by paulftw:


Chapter on Background Indexing ends with

We also plan to add a simpler API soon to check the status of background indexing. See this PR for more details.

But the linked PR is already merged. The docs should be updated to describe the new API, before the next major release is cut

Hi, Paul! The docs are now updated to reflect that this PR has been merged. Thank you for raising this issue :slight_smile: