updated README.md

README.md

@@ -1,3 +1,15 @@
 # HushNixPkgs
 
-Hush packages written for Nix/NixOS
+Hush packages written for Nix/NixOS
+
+## How to build on NixOS
+
+1. Enter directory of package.
+1. Run the following to build it `nix-build -E 'with import <nixpkgs> {}; callPackage ./default.nix {}'`
+
+## How to calculate directory sha256sum
+
+NixOS requires packages to use the directory hash and this can be done as follows:
+1. Download the tar.gz source code and extract.
+1. Then run the following against that directory-name: `nix hash-path directory-name`
+