README updates for clarity re: installation.

README.md

@@ -32,6 +32,21 @@ once by installing our "bundle" [`google-cloud`][bundle-forge] module:
 
     puppet module install google-cloud
 
+Since this module depends on the `googleauth` and `google-api-client` gems,
+you will also need to install those, with
+
+    /opt/puppetlabs/puppet/bin/gem install googleauth google-api-client
+
+If you prefer, you could also add the following to your puppet manifest:
+
+		package { [
+				'googleauth',
+				'google-api-client',
+			]:
+				ensure   => present,
+				provider => puppet_gem,
+		}
+
 ## Usage
 
 ### Credentials