add caveat to check https://lsif.dev/
Created by: northyg
Test plan
Ensured link went to correct place, and was recently made aware that https://lsif.dev/ is the place to check for LSIF status.
This doc update was prompted by Zendesk ticket #7154 in which I had the fun of re-remembering that page existed. I wish I had remembered this before filing an unnecessary bug report for lsif-py