Add man page describing the library

Change-Id: Ic562db3fba921974c903cd6259efd22ae7a1a6f0
Reviewed-on: http://review.couchbase.org/23266
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>