[coreboot] Documenting changes and so on

[Patrick Georgi]

Hi everybody,

during last week's issue with the resource allocator there have been some
remarks about how the change seemed practically invisible despite being on
Gerrit for 2 months and some people suggested that it would be useful to
have better documentation with such changes on why they're done and what
the former situation has been.

I created https://review.coreboot.org/c/coreboot/+/41493 to add this aspect
to the reviewing guidelines, to remind contributors to document and to
invite feedback on the mailing list; to provide suggestions to contributors
where such documentation could end up; and also to make sure that reviewers
feel empowered to ask for more docs and/or discussion (by pointing at the
guidelines if necessary).

I hope this allows improving our review culture so that things don't fall
through the cracks in the future (or at least, less often) without becoming
too rigid (please do not use this section to demand typo fixes discussions
on the list, please ;-) )

Please take a look, comment, disagree, and so on.

Thanks,
Patrick