Manual install page needed swift info

The "manual install" developer doc located here:

http://docs.openstack.org/developer/trove/dev/manual_install.html

did not indicate that you need swift for backups.

I added the swift info.

Change-Id: I23e8565aee7e7036e4e6065e2c22f568e65ca7a7
Closes-Bug: #1342273
Merge "Manual install page needed swift info"