Finish README

README.md

@@ -33,3 +33,37 @@ In your Jekyll site's `flake.nix`:
       };
     };
 }
+```
+
+### Custom Configuration
+
+You can customize the build by providing your own Gemfile, lockfile, and gemset:
+
+```nix
+nix-jekyll-builder.lib.${system}.mkJekyllSite {
+  pname = "my-jekyll-site";
+  version = "1.0.0";  # optional
+  src = ./.;
+  gemfile = ./Gemfile;
+  lockfile = ./Gemfile.lock;
+  gemset = ./gemset.nix;
+}
+```
+
+### Generating gemset.nix
+
+```bash
+# In your project directory with Gemfile present
+nix-shell -p bundix --run "bundix -l"
+```
+
+##  Running Tests
+
+```nix
+nix run .#test
+```
+
+## Requirements
+
+- Nix with flakes enabled
+- Ruby gems specified in your Gemfile