Update README for heka image

Added heka description in the list of
images provided by kolla.

TrivialFix
Change-Id: I28ce2ef185f260b779cb6613b4c6ac458376fa95

README.rst

@@ -62,6 +62,8 @@ As well as these infrastructure components:
   and their endpoints.
 - `MariaDB and Galera <https://mariadb.com/kb/en/mariadb/galera-cluster/>`__ for
   highly available MySQL databases
+- `Heka <http://hekad.readthedocs.org/en/>`__ A distributed and
+  scalable logging system for openstack services.
 
 Docker Images
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