status: Add the 2021q1 status report

This document has had a lot of different fingers on it, as is the case
with all status reports, so it'd be quite an effort to credit everyone.
There's a full log to be found on the freebsd-quarterly github repo
under the freebsd organization, and the commit log should contain the
full list.

Please note that all files for any given report, except _index.adoc,
aren't under explicit maintainership, so if anyone notices problems,
feel free to submit/commit fixes.