_content/doc/gc-guide: incorporate additional feedback
_content/doc/gc-guide: incorporate additional feedback

From comments by 178184bf77e7c5ae86300dd7107a89212029c9e8@google.com on CL 414397.

Change-Id: Ic6a5edbd477dbf6c54b996e652056e2189f727ae
Reviewed-on: https://go-review.googlesource.com/c/website/+/417649
Reviewed-by: Nicolas Hillegeer <178184bf77e7c5ae86300dd7107a89212029c9e8@google.com>
Reviewed-by: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
Reviewed-by: Lasse Folger <c1a9282e9a97d9bcfa578c9e6643dbf90dcebfeb@google.com>

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website