doc/go1.20: add hyperlinks, minor edits
doc/go1.20: add hyperlinks, minor edits

Add links to all significant documentation symbols.
Fix or improve wording a few places.

Change-Id: I53277125eb75a8223a7464136e99accdb46744b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/452757
Reviewed-by: Damien Neil <7e091e9a80da888fcd7836fd3c6b7b85f4677c12@google.com>
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Bypass: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go