README.md: link to Cabal quickstart

Since the REDME so eager to touch on Cabal basics, drive people to official docs
on it.

Author: Anton-Latukha

README.md

@@ -45,6 +45,8 @@ cd hnix
 
 ### Development using Cabal
 
+Cabal [Quickstart](https://cabal.readthedocs.io/en/3.4/nix-local-build.html).
+
 1. (Optional), to enter and work in the reproducible Nix environemt:
 ```
 nix-shell