Added etc-hosts example to readme

Author: Alex-Welsh

elements/etc-hosts/README.rst

@@ -4,3 +4,13 @@ etc-hosts
 Appends text to /etc/hosts.
 
 `DIB_ETC_HOSTS_EXTRA`: Lines to add to /etc/hosts
+
+For example:
+
+  .. code-block::
+
+   export DIB_ETC_HOSTS_EXTRA="192.168.20.1 compute-host-01"
+
+Or:
+
+   export DIB_ETC_HOSTS_EXTRA=`cat ./my-hosts`