Add instruction to contact Psiphon for connection params

MobileLibrary/iOS/USAGE.md

@@ -9,6 +9,10 @@ blocked by censors.
 The Psiphon Library is available as a `.framework` that can be easily included
 in your project using these instructions.
 
+## Using the Psiphon network
+
+In order to use a Psiphon library over the Psiphon network, you need to contact Psiphon to obtain connection parameters to use with your application. Please email us at [info@psiphon.ca](mailto:info@psiphon.ca).
+
 ## Using the Library in your App
 
 **First step:** Review the sample app, located under `SampleApps`.