add portable service docs

Signed-off-by: Xe <me@christine.website>

doc/portable-svc.md

@@ -0,0 +1,59 @@
+# Portable Service
+
+To run this service as a [portable
+service](https://systemd.io/PORTABLE_SERVICES/), you either need to build it
+from source or fetch a premade image from my server. Then you need to activate
+the portable service and manage it like any other systemd service.
+
+## Getting Image
+
+### Building From Source
+
+To build from source, install Nix and enable flakes. Then run this command:
+
+```
+nix build "git+https://tulpa.dev/cadey/printerfacts.git?ref=main#portable-service"
+```
+
+Copy this to somewhere on your target server:
+
+```
+scp $(readlink ./result) target:printerfacts_0.3.1.raw
+```
+
+### Downloading From My Server
+
+Visit [my portable services
+repository](https://xena.greedo.xeserv.us/pkg/portable/) server and download the
+most recent `printerfacts` `.raw` file. Put it somewhere on the target machine.
+
+## Installing and Activating
+
+If you are running Ubuntu 22.04, you will need to install `systemd-portabled`:
+
+```
+sudo apt -y install systemd-container
+```
+
+This may work on other distros, but I have only tested this on Ubuntu 22.04.
+
+Then attach the service image:
+
+```
+sudo portablectl attach ./printerfacts_0.3.1.raw
+```
+
+And activate it like any other systemd service:
+
+```
+sudo systemctl enable --now printerfacts.service
+```
+
+And then fetch a printer fact:
+
+```
+$ curl http://[::1]:32042/fact
+On average, a printer will sleep for 16 hours a day.
+```
+
+Or open it in your browser: http://target:32042