src: continued use of Subversion for getting updates

[Theron]

On 1/3/21 12:02 AM, Theron wrote:
> On 12/23/20 3:49 AM, Warner Losh wrote:
>> I'm all ears on ways to make the docs better
> I think a heads-up on the Git move and how to stay up to date in 
> /usr/src/UPDATING is needed.  I was surprised to find no mention there.

Oops, I did mean to say "UPDATING in subversion".

20201223:
     The FreeBSD project has migrated from Subversion to Git. Temporary
     instructions can be found at
     https://github.com/bsdimp/freebsd-git-docs/blob/main/src-cvt.md
     and other documents in that repo.

So it's there in Git.  In that case I think this should be copied to 
https://svn.freebsd.org/base/head/UPDATING ASAP (unless that completely 
breaks future migration in some way).