ACL2 release info

[Matt Kaufmann]

Hi acl2-books --

By now you've probably seen the email announcing the release of ACL2
Version 8.7. Just to be clear, though, I haven't yet merged
that into the ACL2 github repository -- I'll run tests first, after
putting back the usual startup banner.

Soon you will be able to use git to get the new release by using the
following commands to create a fresh subdirectory, DIR, containing
that release. (BUT I can easily imagine that nobody will want to do
that, including me.)

git clone https://github.com/acl2/acl2 DIR
cd DIR
git checkout 8.7

But I believe that until I do the first commit/push to the normal
repo, that tag won't exist for that repo. I'm hoping to do that
commit/push within the next day.

-- Matt