Update third_party.md with Zig implementation (#14192)

Proposition to add my own implementation of protobuf for the Zig programming language.

Closes #14192

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/14192 from Arwalk:patch-1 d48281d61ab1e1a34d9c50f26ceaa011c2755132
PiperOrigin-RevId: 568232767
diff --git a/docs/third_party.md b/docs/third_party.md
index e3095a5..ed63375 100644
--- a/docs/third_party.md
+++ b/docs/third_party.md
@@ -124,6 +124,7 @@
 *   Typescript: https://github.com/pbkit/pbkit
 *   Vala: https://launchpad.net/protobuf-vala
 *   Visual Basic: https://code.google.com/p/protobuf-net/
+*   Zig: https://github.com/Arwalk/zig-protobuf
 
 ## RPC Implementations