Remove outdated instructions for adding languages (#11005)

This PR removes the outdated comment regarding adding languages to Zed.

New languages should be added as extensions.

Release Notes:

- N/A
7005f0b424Marshall Bowers committed on 4/25/2024, 6:30:31 PM· committed by GitHubparentd3f6ca7
1 file changedLine totals unavailable