add reference to project team guide for openstack projects
add reference to project team guide for openstack projects

We do not want to put instructions that are specific to OpenStack in a
general-purpose tool, but it's OK to link to those instructions
elsewhere since a lot of people will start by looking at the reno
documentation.

Change-Id: I73f9fd71cfc24d67420adb70509a2775ad022627
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

openstack/reno