Background
It's possible to read the current "Sending a change via GitHub" section of the Contribution Guide as saying a Gerrit account is optional when sending a GitHub PR. The closest it comes to explicitly telling someone to use Gerrit might be:
Remember you can always visit Gerrit to see the fine-grained review.
Perhaps avoiding the requirement of a Gerrit account was an aspirational goal when that section was written, or perhaps that is an unintended reading.
Outside of the "Sending a change via GitHub" section, the contribution guide does say a Gerrit account is required, but that seems to be intermixed with various other steps that are not required for a GitHub-based workflow, and hence can be read as not applying to the GitHub-based workflow.
I think experience suggests that a Gerrit account is almost always needed, including to write a reply to reviewers, mark feedback as done, and so on. Some of the friction listed by Bryan in https://github.com/golang/go/discussions/61182 seems to be the result of GitHub users not registering for Gerrit.
Suggestion
We should make it clear that a Gerrit account is considered a requirement even if sending a PR via GitHub.
The potential contributor must use a Gmail or other Google account to sign the CLA, so registering for Gerrit is hopefully a very small additional step at that point. A Gerrit account of course also serves as an on-ramp to more use of Gerrit, including possibly helping review other CLs or using the pure Gerrit contribution workflow.
To help make this suggestion more concrete, I will send a draft CL shortly.
Comment From: gopherbot
Change https://go.dev/cl/509019 mentions this issue: _content/doc/contribute: make it clear a Gerrit account is required even when sending a GitHub PR
Comment From: thepudds
Rough draft for discussion purposes in https://go.dev/cl/509019.
CC @heschi, @cagedmantis