Document possible values for DD_SITE (#110)

Author: tianchu

README.md

@@ -61,7 +61,7 @@ api._api_key = "MY_API_KEY"
 
 ### DD_SITE
 
-If `DD_FLUSH_TO_LOG` is set to `false` (not recommended), and your data need to be sent to the Datadog EU site, you must set `DD_SITE` to `datadoghq.eu`. Defaults to `datadoghq.com`.
+If `DD_FLUSH_TO_LOG` is set to `false` (not recommended), you must set `DD_SITE`. Possible values are `datadoghq.com`, `datadoghq.eu`, `us3.datadoghq.com` and `ddog-gov.com`. The default is `datadoghq.com`.
 
 ### DD_LOGS_INJECTION