add brief explanation to .flux.env.example

docs/installation/install_oas.rst

@@ -58,7 +58,7 @@ Prerequisites
 Copy the file ``install/.flux.env.example`` to your cluster dir
 ``clusters/oas.example.org/.flux.env``. This file contains the last bit of
 information you need to configure. You **have to** configure the following
-values. The rest are optional. 
+values. The rest are optional.
 
 - ``ip_address``: The IP address of your cluster
 - ``domain``: The FQDN of your cluster

install/.flux.env.example

+# This file contains variables that will be used in Kubernetes manifests.
+# Replace the values to make sense for your setup. The values should not be
+# quoted (correct: a=b, incorrect: a="b").
+
 # IP address of the cluster
 ip_address=1.2.3.4
 # FQDN of the cluster