doc/start: add section for using mkflake

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 Devos as a library!](./mkflake.md)
 
 
 [install-nix]: https://nixos.org/manual/nix/stable/#sect-multi-user-installation

doc/start/mkflake.md

@@ -0,0 +1,42 @@
+# Use Devos as a library!
+You can also add devos as a flake input and use its library function, `mkFlake` to 
+create your flake. This gives you the advantage of using nix flakes to sync with 
+upstream changes in devos.
+
+You can either use the default template or use the 'mkflake' template which only
+includes the necessary folders for `mkFlake` usage. It can be pulled with:
+```sh
+nix flake init -t github:divnix/devos#mkflake
+```
+
+Once you have a template, you need to add devos as a flake input, which would look
+like this:
+```nix
+inputs = {
+  ...
+  devos.url = "github:divnix/devos";
+};
+```
+> ##### Note:
+> - All devos inputs must still be included in your flake, due to a nix
+>   [issue](https://github.com/NixOS/nix/pull/4641) with the `follows` attribute.
+> - You can append `/community` to access community modules [extern](../../extern).
+
+You can then call `mkFlake` to create your outputs. Here is a simple example:
+```nix
+outputs = { self, devos, ... }: devos.lib.mkFlake { 
+  inherit self; 
+  hosts = ./hosts;
+};
+```
+`mkFlake` has various arguments to include more devos concepts like suites and profiles.
+These options are documented in (mkFlakeOptions)[../mkFlakeOptions.md].
+
+The devos template itself uses mkFlake to export its own outputs, so you can take
+a look at this repository's [flake.nix](../../flake.nix) for a more realistic use
+of `mkFlake`.
+
+You can now sync with upstream devos changes just like any other flake input. But
+you will no longer be able to edit devos's internals, since you are directly following
+upstream devos changes.
+