updated readme with structure.

README.md

@@ -1,3 +1,29 @@
 # nix-config
 
 My configs for both nixos and home manager only machines
+
+## structure
+
+```
+.
+├── flake.nix
+├── configs
+│   ├── home-manager
+│   └── nixos
+├── hosts
+├── modules
+│   ├── home-manager
+│   └── hostopts.nix
+├── roles
+│   ├── home-manager
+│   └── nixos
+└── templates
+```
+* Configs set options and specify programs to be installed.
+They do not specify their own options, and take effect as soon as they are imported.
+Generally, a config will be specific to a single program, and possibly optional dependecies of the main program.
+* Hosts define specific hosts. They are the entry point into the system.
+Each host *must* import `configs/nixos/common.nix` in the top level and `configs/home-manager/common.nix` in the home-manager block.
+Each host *must also* define the variables declared in `modules/hostopts.nix`.
+* Modules are always imported by the respective common.nix. They each have an enable option, and only have effects if enabled.
+* Roles are larger bundles of software and options. They define packages to be installed and may import configurations or enable modules.