Reminder: juju-core github migration

[Ian Booth]

Hi folks

As per previous communications, we'll be migrating the juju-core codebase off
Launchpad and across to Github at 10:00 UTC Tuesday 3 June.

Here's a link to the new Contributing document which describes the new landing
workflow:

https://raw.githubusercontent.com/bz2/core/4a7de7b9a52bab794821766e40503a66ca08fcaa/CONTRIBUTING

Essentially, you:

1. Create a pull request against github.com/juju/core master
2. A reviewer indicates that the pull request is LGTM
3. A member of the Juju project adds a comment containing $$merge$$ to initiate
the landing process.
4. An email will be sent with a link to the Jenkins job running the tests.
5. An email will be sent when the tests either pass (and the merge is done) or fail.

Please try and have all work landed into trunk by the cutover time. A brief set
of steps will be sent out describing how to migrate any current work in progress
across to Github.

Any questions between and the cutover, trying pinging mgz or myself (wallyworld)
on #juju-dev.