docs: add networking (#4030)

docs/networking/port-forwarding.md

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+# Port Forwarding
+
+Port forwarding lets developers securely access processes on their Coder
+workspace from a local machine. A common use case is testing web
+applications in a browser.
+
+There are two ways to forward ports in Coder:
+
+- The `coder port-forward` command
+- SSH
+
+The `coder port-forward` command is generally more performant.
+
+## coder port-forward
+
+Forward the remote TCP port `8080` to local port `8000` like so:
+
+```console
+coder port-forward myworkspace --tcp 8000:8080
+```
+
+For more examples, see `coder port-forward --help`.
+
+## SSH
+
+First, [configure SSH](../ides.md#ssh-configuration) on your
+local machine. Then, use `ssh` to forward like so:
+
+```console
+ssh -L 8080:localhost:8000 coder.myworkspace
+```
+
+You can read more on SSH port forwarding [here](https://www.ssh.com/academy/ssh/tunneling/example).