Fix env-generator doc formatting

Bulleted lists must have whitespace before and after or they don't
render properly.

Change-Id: I7dcc58b8d9e02d99918bbdcc7d0fc3905d66f71c

sample-env-generator/README.rst

@@ -24,10 +24,12 @@ entries in the files can be used as examples, and a more detailed
 explanation of the different available keys is below:
 
 Top-level:
+
 - **environments**: This is the top-level key in the file.  All other keys
   below should appear in a list of dictionaries that define environments.
 
 Environment-specific:
+
 - **name**: the output file will be this name + .yaml, in the
   ``environments`` directory.
 - **title**: a human-readable title for the environment.