doc/start: add use-mkdevos section

doc/start/index.md

@@ -36,6 +36,7 @@ In addition, the [binary cache](../../cachix) is added for faster deployment.
 - [Make installable ISO](./iso.md)
 - [Bootstrap Host](./bootstrapping.md)
 - [Already on NixOS](./from-nixos.md)
+- [Use mkDevos](./mkDevos.md)
 
 
 [install-nix]: https://nixos.org/manual/nix/stable/#sect-multi-user-installation

doc/start/use-mkdevos.md

@@ -0,0 +1,31 @@
+# Use mkDevos
+You can also use devos as a flake input and get the advantage of using
+nix flakes to sync with upstream changes in devos.
+
+To do this you will need the template and nix unstable. Edit your flake.nix to
+add devos as an input:
+```nix
+inputs = {
+  ...
+  devos.url = "github:divnix/devos";
+};
+```
+then replace the outputs section with this:
+```nix
+outputs = { self, devos, ... }: devos.lib.mkDevos { inherit self; };
+```
+
+Now you can update devos as you would any other flake input:
+```sh
+nix flake update --update-input devos
+```
+
+> ##### Notes:
+> - All inputs used in devos must also be added to your flake, due to an
+>   [issue](nixos/nix#4641) with nix.
+> - Optionally, you can safely delete [lib](../../lib) and [tests](../../tests) and
+>   the [core profile](../../profiles/core)
+> - You can append `/community` to the `devos.url` to get access to community modules
+>   which can be added in [extern](../../extern).
+> - To use community profiles, you will have to copy them to your tree
+> - If you use this method, you will no longer be able to edit devos internals.