Add Zig impl to README (#364)

Author: GrapeBaBa

README.md

@@ -82,6 +82,8 @@ The `validate.py` script can be used to validate the table once it's edited.
   - [copper-multicodec](https://github.com/filip26/copper-multicodec)
 - Kotlin
   - `multicodec` part of Kotlin project [multiformat](https://github.com/erwin-kok/multiformat)
+- Zig
+  - `multicodec` part of Zig project [multiformats-zig](https://github.com/optimism-java/multiformats-zig)
 - [Add yours today!](https://github.com/multiformats/multicodec/edit/master/table.csv)
 
 ## Reserved Code Ranges