doc/faq: update FAQ

The FAQ had some old bits that were no longer accurate, let alone
helpful, such as talking about running godoc, while also being behind
the times on things like cloud usage.

Also some text deserved rephrasing.

Fixes golang/go#64919

Change-Id: I133c996be4dd4370566a0a4d7512805d05a34201
Reviewed-on: https://go-review.googlesource.com/c/website/+/556915
Run-TryBot: Rob Pike <[email protected]>
Reviewed-by: Eli Bendersky <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Russ Cox <[email protected]>

Author: robpike