docs: add more info around how to test via VMs

docs/commands/testing.md

@@ -4,8 +4,27 @@ SPDX-FileCopyrightText: Andrew Hayzen <[email protected]>
 SPDX-License-Identifier: MPL-2.0
 -->
 
+# Test with flake check
+
+We need the sandbox disabled as we need network access
+
+```console
+$ nix flake --option sandbox false check -L --show-trace
+```
+
 # Test in a VM
 
+Ensure that you add the following snippet to the configuration of the machine you want to test in a VM.
+
+```nix
+{
+    ahayzen.testing = true;
+}
+```
+
+> Note that if you are testing http update any `Caddyfile.vm` to use `http://localhost`
+> rather than `http://mydomain.com` to access locally.
+
 ## `nixos-build`
 
 ```console
@@ -31,11 +50,3 @@ $ result/bin/run-<machine>-vm
 ```console
 $ ssh -oUserKnownHostsFile=/dev/null -oStrictHostKeyChecking=no admin@localhost -p 2221
 ```
-
-## Flake check
-
-We need the sandbox disabled as we need network access
-
-```console
-$ nix flake --option sandbox false check -L --show-trace
-```