docs: add note about NO_PROXY env variable
Deno supports proxies for module downloads and the Web standard `fetch` API.
-Proxy configuration is read from environmental variables: `HTTP_PROXY` and
-`HTTPS_PROXY`.
+Proxy configuration is read from environmental variables: `HTTP_PROXY`,
+`HTTPS_PROXY` and `NO_PROXY`.
In case of Windows, if environment variables are not found Deno falls back to
reading proxies from registry.
