Fix throttling documentation about Remote-Addr (#5414)

Clarify in docs that REMOTE_ADDR is part of the WSGI environ, not an HTTP header.

docs/api-guide/throttling.md

@@ -68,9 +68,9 @@ Or, if you're using the `@api_view` decorator with function based views.
 
 ## How clients are identified
 
-The `X-Forwarded-For` and `Remote-Addr` HTTP headers are used to uniquely identify client IP addresses for throttling.  If the `X-Forwarded-For` header is present then it will be used, otherwise the value of the `Remote-Addr` header will be used.
+The `X-Forwarded-For` HTTP header and `REMOTE_ADDR` WSGI variable are used to uniquely identify client IP addresses for throttling.  If the `X-Forwarded-For` header is present then it will be used, otherwise the value of the `REMOTE_ADDR` variable from the WSGI environment will be used.
 
-If you need to strictly identify unique client IP addresses, you'll need to first configure the number of application proxies that the API runs behind by setting the `NUM_PROXIES` setting.  This setting should be an integer of zero or more.  If set to non-zero then the client IP will be identified as being the last IP address in the `X-Forwarded-For` header, once any application proxy IP addresses have first been excluded.  If set to zero, then the `Remote-Addr` header will always be used as the identifying IP address.
+If you need to strictly identify unique client IP addresses, you'll need to first configure the number of application proxies that the API runs behind by setting the `NUM_PROXIES` setting.  This setting should be an integer of zero or more.  If set to non-zero then the client IP will be identified as being the last IP address in the `X-Forwarded-For` header, once any application proxy IP addresses have first been excluded.  If set to zero, then the `REMOTE_ADDR` value will always be used as the identifying IP address.
 
 It is important to understand that if you configure the `NUM_PROXIES` setting, then all clients behind a unique [NAT'd](http://en.wikipedia.org/wiki/Network_address_translation) gateway will be treated as a single client.