doc/FAQ: Document proxy environment variables

Author: nhooyr

doc/FAQ.md

@@ -27,6 +27,7 @@
 - [Isn't an install script piped into sh insecure?](#isnt-an-install-script-piped-into-sh-insecure)
 - [How do I make my keyboard shortcuts work?](#how-do-i-make-my-keyboard-shortcuts-work)
 - [Differences compared to Theia?](#differences-compared-to-theia)
+- [`$HTTP_PROXY`, `$HTTPS_PROXY`, `$NO_PROXY`](#http_proxy-https_proxy-no_proxy)
 - [Enterprise](#enterprise)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
@@ -338,6 +339,30 @@ You can't just use your VS Code config in Theia like you can with code-server.
 To summarize, code-server is a patched fork of VS Code to run in the browser whereas
 Theia takes some parts of VS Code but is an entirely different editor.
 
+## `$HTTP_PROXY`, `$HTTPS_PROXY`, `$NO_PROXY`
+
+code-server supports the standard environment variables to allow directing
+server side requests through a proxy.
+
+```sh
+export HTTP_PROXY=https://134.8.5.4
+export HTTPS_PROXY=https://134.8.5.4
+# Now all of code-server's server side requests will go through
+# https://134.8.5.4 first.
+code-server
+```
+
+- See [proxy-from-env](https://www.npmjs.com/package/proxy-from-env#environment-variables)
+  for a detailed reference on the various environment variables and their syntax.
+  - code-server only uses the `http` and `https` protocols.
+- See [proxy-agent](https://www.npmjs.com/package/proxy-agent) for the various supported
+  proxy protocols.
+
+**note**: Only server side requests will be proxied! This includes fetching extensions,
+requests made from extensions etc. To proxy requests from your browser you need to
+configure your browser separately. Browser requests would cover exploring the extension
+marketplace.
+
 ## Enterprise
 
 Visit [our enterprise page](https://coder.com) for more information about our