Apache Isis source code (master) is now hosted at github

[Dan Haywood <da...@haywood-associates.co.uk>]

Dear committers (and any one else),

just to say that as per INFRA-15082, ASF infra have now moved the Apache
Isis git repo, and the master is now hosted at github, ie it is no longer a
mirror.

If you want to push changes to our repo, you'll therefore need to:

a) on your local clone, update the origin to be
https://github.com/apache/isis.git (just edit .git/config).

b) link your ASF and github accounts and enable 2FA, as per
https://gitbox.apache.org/setup/

This also lets PRs be applied directly via the github repo.  I'm not
certain what other features are available to us ... for example we could
use github issues rather than JIRA, and/or the "projects" feature.  But,
for now, one thing at a time, I think.

Thx
Dan