improve readme

README.md

@@ -1,9 +1,18 @@
-Features:
+## corenix
 
-- Specify config overrides as Nix attribute set
-- Change payload without rebuilding coreboot
+*How to use:*
 
-Limitations:
+1. Create a configuration file for your device in `configs/`
+2. Add an entry to flake.nix, i.e. `my-device = makeDevice ./configs/my-device.nix;`
+3. Build the coreboot rom: `nix build .#my-device`
+
+*Features*
+
+- Specify the build parameters with NixOS-style modules
+- Share declarative configuration across devices
+- Use cached coreboot and payload builds for different device/payload combinations
+
+*Limitations*
 
 - currently only `x86_64-linux` host and target systems are supported
-- It's not yet possible to build with a SeaBIOS payload
+- Only GRUB2 and TianoCore payloads are supported for now