CCBC-181 Add more complete example to lcb_observe(3) manpage

Change-Id: I1014f146c5fbd3d3b82e7bef6edc06f10055ee02
Reviewed-on: http://review.couchbase.org/28067
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>