Harmonize the cross repo advice.

[imp]

Summary

The other committer's guide was written years before the cross repo
commit bit stuff. Harmonize and expand a little the advice given to make
it also match the tone of the new policy and our usual practices being a
little more relaxed than what was documented previously.

Sponsored by: Netflix

[jhb]

documentation/content/en/articles/committers-guide/_index.adoc

272–284

I wonder if we want to relax this to "All committers" vs just Doc? I'm fine with keeping the existing language though.

2645

I really want this case to just be "Reviewed by;" and not "Approved by:". That is, the point is to get review of the change itself not permission to commit a change separate from reviewing it.

[imp]

jhb's changes