gopls/doc: add documentation for "local" configuration
gopls/doc: add documentation for "local" configuration

Change-Id: I9181c986b8e5aa21526ff934b62c041f3c820b7c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/224117
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools