update readme

Author: Philip Reichenberger

README.md

@@ -13,4 +13,10 @@ func getClient() *paperspace.Client {
     client.APIKey = p.APIKey
     return client
 }
-```
+```
+
+## Environment Variables
+- PAPERSPACE_APIKEY: Paperspace API key
+- PAPERSPACE_BASEURL: Paperspace API url
+- PAPERSPACE_DEBUG: Enable debugging
+- PAPERSPACE_DEBUG_BODY: Enable debug for response body