docs(docs/dev/add_host): add sketch notes about adding new hosts

docs/dev/add_host.adoc

@@ -0,0 +1,38 @@
+= os.dev.add-host(8)
+
+== Name
+
+os.dev.add-host - Add a new host
+
+== Configuration
+
+To add a new host, complete the following steps:
+
+. Add the new host configuration to the `hosts/<HOST>` directory
+. Update the `flake.nix` packages and checks
+. Update the `hosts/default.nix` file
+
+== Deployment
+
+To deploy a new host, complete the following steps based on the more complete
+instructions given in `hosts/<HOST>/README.adoc`:
+
+. Clone Repository
+. Format all Disks
+. Update Hardware Configuration
+. Install NixOS
+. `poweroff`
+
+Properly deploying `agenix` requires adding the public SSH key of the new host
+to the `secrets.nix` file, and re-keying all secrets, using `agenix --rekey`.
+The SSH keys can be deployed in two ways. Either the SSH keys is generated and
+added the repository prior to the installation process, or the SSH keys are
+generated during the installation, although this requires patching upstream
+during the installation process.
+
+Although the generated hardware configuration should be patched upstream, it can
+also be done at a later point, as the installation can be completed by
+overwriting the template hardware configuration in the local repository clone.
+Make sure to that the hardware configuration does not disappear after the
+installation process, by for example adding it to an external drive or storing
+it in the `/persistent` directory.