Guide: fix zig pkg-add example

docs/acton-by-example/src/zig_dependencies.md

@@ -2,6 +2,28 @@
 
 Much like dependencies on other Acton packages, an Acton project can depend on a Zig package which could be a C / C++ or Zig library, as long as it has a `build.zig` file.
 
-- `acton zig-pkg add URL NAME --artifact X --artifact`
+- `acton zig-pkg add URL NAME --artifact X --artifact Y`
   - list the libraries you want to link with as artifacts
 - `acton zig-pkg remove NAME`
+
+~~~admonish example
+```
+acton zig-pkg add https://github.com/allyourcodebase/zlib/archive/refs/tags/1.3.1.tar.gz zlib --artifacts z
+```
+
+```json
+{
+    "dependencies": {},
+    "zig_dependencies": {
+        "zlib": {
+            "url": "https://github.com/allyourcodebase/zlib/archive/refs/tags/1.3.1.tar.gz",
+            "hash": "122034ab2a12adf8016ffa76e48b4be3245ffd305193edba4d83058adbcfa749c107",
+            "artifacts": [
+                "z"
+            ]
+        }
+    }
+}
+```
+
+~~~