add documentation

README.md

@@ -47,6 +47,27 @@ NOTE: it sometimes takes a while for the services to start up, and in the meanti
     pixelfed-manage user:create --name=test --username=test --email=test@test.com --password=testtest --confirm_email=1
     ```
 
+# Building an installer image
+
+Build an installer image for the desired configuration, e.g. for `peertube`:
+
+```bash
+nix build .#installers.peertube
+```
+
+Upload the image in `./result` to Proxmox when creating a VM.
+Booting the image will format the disk and install NixOS with the desired configuration.
+
+# Deploying an updated machine configuration
+
+> TODO: There is currently no way to specify an actual target machine by name.
+
+Assuming you have SSH configuration with access to the remote `root` user stored for a machine called e.g. `peertube`, deploy the configuration by the same name:
+
+```bash
+nix run .#deploy.peertube
+```
+
 ## debugging notes
 
 - it is sometimes useful to `cat result/bin/run-nixos-vm` to see what's really going on (e.g. which ports are getting forwarded)