Add Sorbet troubleshooting note

[andyw8]

Motivation

Document this implicit Ruby LSP behavior for the benefit of users trying to set up or troubleshoot their editor.

Implementation

Add a note to the docs.

Automated Tests

n/a

Manual Tests

n/a

[andyw8]

cc @ChallaHalla

[vinistock]

We should also check if the user has the Sorbet extension and, if not, enforce that our features will be enabled.

[andyw8]

We should also check if the user has the Sorbet extension and, if not, enforce that our features will be enabled.

Yes: #2856