Add Changelog to the documentation

Include the ChangeLog generated by pbr in the documentation

Closes-Bug: 1336974

Change-Id: I2f2cb935dc52d5d0e9ddc4439a0022f739776f45
Signed-off-by: Rosario Di Somma <rosario.disomma@dreamhost.com>
Merge "Add Changelog to the documentation"