[infra] Update docs with respect to Go modules.

Docs-Preview: https://skia.org/?cl=255085
Change-Id: I8911862ca9814b89b8598ad743b1faa9c524399f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255085
Commit-Queue: Ben Wagner aka dogben <benjaminwagner@google.com>
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Auto-Submit: Ben Wagner aka dogben <benjaminwagner@google.com>
3 files changed