Update docs for pull request creation

Author: gonchik

docs/bitbucket.rst

@@ -139,6 +139,9 @@ Manage code
     # Add comment into pull request
     bitbucket.add_pull_request_comment(project, repository, pull_request_id, text)
 
+    # Create a new pull request between two branches.
+    bitbucket.open_pull_request(source_project, source_repo, dest_project, dest_repo, source_branch, destination_branch, title, description)
+
     # Get tags for related repo
     bitbucket.get_tags(project, repository, filter='', limit=99999)