Add us5 to the README (#169)

Author: agocs

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), you must set `DD_SITE`. Possible values are `datadoghq.com`, `datadoghq.eu`, `us3.datadoghq.com` and `ddog-gov.com`. The default is `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`, `us5.datadoghq.com`, and `ddog-gov.com`. The default is `datadoghq.com`.
 
 ### DD_LOGS_INJECTION