readme: add notice for legacy interface

README.md

@@ -13,6 +13,10 @@
 
 !!! Warning: dream2nix is unstable software. While simple UX is one of our main focus points, the APIs  are still under development. Do expect changes that will break your setup.
 
+### legacy dream2nix
+
+Dream2nix is currently in the process of re-factoring it's modules to make use of drv-parts. Not all features and subsystmes are migrated yet. If you prefer continue using the `makeFlakeOutputs` interface, please refer to the `[legacy branch](https://github.com/nix-community/dream2nix/tree/legacy) of dream2nix.
+
 ### Funding
 
 This project was funded through the [NGI Assure](https://nlnet.nl/assure) Fund, a fund established by [NLnet](https://nlnet.nl/) with financial support from the European Commission's [Next Generation Internet](https://ngi.eu/) programme, under the aegis of DG Communications Networks, Content and Technology under grant agreement No 957073. **Applications are still open, you can [apply today](https://nlnet.nl/propose)**.