Adding a MAINTAINERS file

[Brendan Higgins]

For those who were not present, there was an OpenBMC meetup of sorts
last week. One issue that Nancy Yuen, Abhishek Pandit, and myself
brought up for non-IBM contributors was ownership and organization of
projects; this went in a couple directions, but at some point somebody
proposed a Linux kernel style MAINTAINERS list as a way to find people
relevant for discussions in the various sub-parts of the project.

I made an initial implementation: https://gerrit.openbmc-project.xyz/#/c/944/

Most of it should be pretty self-explanatory (if not please join in
the discussion). Nevertheless, I distinguished between reviewers and
maintainers; whereas a reviewer is someone who is familiar enough with
a given part of a project that she is a good person to address
questions to concerning that component and should be included on code
reviews; a maintainer is someone who's approval is required to check a
patch set into a repository.

I chose reviewers based on the amount of commits contributed to a
given repository; I know this is not the best way to decide whether
someone should be considered an expert on a particular part of the
code base, but I thought it was a reasonable place to start.
Additionally, breaking things up only at the repo level is probably
also not the most useful as people may become experts within a
particular part of a given repository, but again I think this is a
reasonable starting place and I added semantics for breaking it down
further.

For maintainers, I chose two people for each repository; the first is
the person who already has the authoritative access I described above;
the second was chosen to be a major contributor. For Linux, u-boot,
ipmi-tool, and qemu that is some combination of Joel, Cédric, and
Jeremy. For everything else, all of the userland stuff and yocto, that
is Patrick and Brad. I recall discussing adding Brad as a maintainer
for the userland stuff in the meeting, but I figure it is something we
should also discuss on the email list for everyone's benefit. We had
not discussed adding a second maintainer for anything else, but I
figure it is probably best practice to have more than once person who
can submit code in all cases.

I fully expect that the MAINTAINERS file I uploaded will require a
good deal of discussion before it is ready to submit, but I figured it
would be easiest to start with something to talk over.

Cheers