Allow to set throttle category to the job

This patch allows to map specific job with pre-created
category.

Change-Id: Ie5ec841af6a1d73959e760471d7ed00ac7c3f882
diff --git a/README.rst b/README.rst
index ec59304..41520e3 100644
--- a/README.rst
+++ b/README.rst
@@ -471,7 +471,10 @@
               throttleconcurrents:
                 enabled: True
                 max_concurrent_per_node: 3
-                max_concurrent_total: 5
+                max_concurrent_total: 1
+                throttle_option: category #one of project (default or category)
+                categories:
+                  - my_throuttle_category
         plugin:
           swarm:
             restart: false