Describe how to create design document

In reply to http://www.couchbase.com/forums/thread/create-view-c-api

Change-Id: I05e6c1b6e5df64c2820e176d60b40edd85296d3d
Reviewed-on: http://review.couchbase.org/24892
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>