doc: add new doc website

* use mmdoc
* add github pages action to auto publish
* do not edit README for now, will follow up with a commit directs
people to the doc site

doc/install-via-flakes.md

@@ -0,0 +1,39 @@
+# Install via Flakes {#install-via-flakes}
+
+## Install module via Flakes
+
+```nix
+{
+  inputs.agenix.url = "github:ryantm/agenix";
+  # optional, not necessary for the module
+  #inputs.agenix.inputs.nixpkgs.follows = "nixpkgs";
+
+  outputs = { self, nixpkgs, agenix }: {
+    # change `yourhostname` to your actual hostname
+    nixosConfigurations.yourhostname = nixpkgs.lib.nixosSystem {
+      # change to your system:
+      system = "x86_64-linux";
+      modules = [
+        ./configuration.nix
+        agenix.nixosModules.default
+      ];
+    };
+  };
+}
+```
+
+## Install CLI via Flakes
+
+You don't need to install it,
+
+```ShellSession
+nix run github:ryantm/agenix -- --help
+```
+
+but, if you want to (change the system based on your system):
+
+```nix
+{
+  environment.systemPackages = [ agenix.packages.x86_64-linux.default ];
+}
+```