add note about host format by @cwest144

Author: derpoho

README.md

@@ -77,6 +77,9 @@ $pinecone = new Pinecone($apiKey, $indexHost);
 // all control AND data methods are available now
 ```
 
+> **Info**
+> The index host should include `https://`, which you may need to prepend to the value returned from Pinecone.
+
 ## Responses
 
 All responses are returned as a `Response` object.