Added missing documentation

- Adding documentation for config options
- Adding contact information to README.rst

Change-Id: I966bc07071b13e93cbc3274a9ef91280117d8dba
Partial-Bug: #1568178

README.rst

@@ -12,6 +12,8 @@ which will enable smarter scheduling and environmental service assurance monitor
 * Documentation: http://docs.openstack.org/developer/collectd-ceilometer-plugin
 * Source: http://git.openstack.org/cgit/openstack/collectd-ceilometer-plugin
 * Bugs: http://bugs.launchpad.net/collectd-ceilometer-plugin
+* Contact: E-mail the dev mailing list with the [collectd-ceilometer-plugin] tag
+           mailto:openstack-dev@lists.openstack.org?subject=[collectd-ceilometer-plugin]
 
 Features
 --------

doc/source/usage.rst

@@ -24,3 +24,19 @@ COLLECTD_INSTALL
     Set this to False if you are running a custom collectd build or do not
     want to upgrade installed version.
     Default: True
+
+
+COLLECTD_BATCH_SIZE
+    Set the amount of samples to be buffered before sending.
+    Default: 1 i.e. no batching/buffering.
+
+
+COLLECTD_DIR
+    Specify collectd directory, this is required if collectd was installed
+    manually.
+    Default: /opt/collectd
+
+
+CEILOMETER_TIMEOUT
+    Sets the ceilometer's request timeout. The value is passed in milliseconds.
+    Default: 1000 i.e. 1 sec.