Mention NO_PROXY environment variable on Advanced Usage page (#3066)

Co-authored-by: Kar Petrosyan <[email protected]>

Author: RichieB2B

docs/advanced/transports.md

@@ -329,4 +329,5 @@ mounts = {
 There are also environment variables that can be used to control the dictionary of the client mounts. 
 They can be used to configure HTTP proxying for clients.
 
-See documentation on [`HTTP_PROXY`, `HTTPS_PROXY`, `ALL_PROXY`](../environment_variables.md#http_proxy-https_proxy-all_proxy) for more information.
+See documentation on [`HTTP_PROXY`, `HTTPS_PROXY`, `ALL_PROXY`](../environment_variables.md#http_proxy-https_proxy-all_proxy)
+and [`NO_PROXY`](../environment_variables.md#no_proxy) for more information.