Update guide_gce.rst

Make the docs more specific.

docsite/rst/guide_gce.rst

@@ -22,7 +22,7 @@ The GCE modules all require the apache-libcloud module, which you can install fr
 Credentials
 -----------
 
-To work with the GCE modules, you'll first need to get some credentials. You can create new one from the `console <https://console.developers.google.com/>`_ by going to the "APIs and Auth" section and choosing to create a new client ID for a service account. Once you've created a new client ID and downloaded the generated private key (in the `pkcs12 format <http://en.wikipedia.org/wiki/PKCS_12>`_), you'll need to convert the key by running the following command:
+To work with the GCE modules, you'll first need to get some credentials. You can create new one from the `console <https://console.developers.google.com/>`_ by going to the "APIs and Auth" section and choosing to create a new client ID for a service account. Once you've created a new client ID and downloaded (you must click **Generate new P12 Key**) the generated private key (in the `pkcs12 format <http://en.wikipedia.org/wiki/PKCS_12>`_), you'll need to convert the key by running the following command:
 
 .. code-block:: bash
 
@@ -79,6 +79,8 @@ Create a file ``secrets.py`` looking like following, and put it in some folder w
     GCE_PARAMS = ('i...@project.googleusercontent.com', '/path/to/project.pem')
     GCE_KEYWORD_PARAMS = {'project': 'project_id'}
 
+Ensure to enter the email adress from the created services account and not the one from your main account.
+
 Now the modules can be used as above, but the account information can be omitted.
 
 GCE Dynamic Inventory