Add doc/build to .gitignore

Generated docs should be ignored, so adding doc/build to gitignore

Change-Id: I4fc03244df37f63351ec1e54b1bcd5b9b3790f5c
Update developer docs template

The current developer docs template used by ceilometer client is
not the latest template used by the rest of the openstack projects.
This patch will update the docs to provide a more consistent look
and feel when using project docs.

Change-Id: Ic25324da75100c0efe3e814de13807740592d4a1