Add grpcmd-gui to Community Showcase (#3994)

Author: AkshayKalose

website/docs/community/showcase/grpcmd-gui.mdx

@@ -0,0 +1,10 @@
+# grpcmd-gui
+
+```mdx-code-block
+<p style={{ "text-align": "center" }}>
+  <img src={require("@site/static/img/showcase/grpcmd-gui.webp").default} />
+  <br />
+</p>
+```
+
+[grpcmd-gui](https://grpc.md/gui) is a modern cross-platform desktop app and API client for gRPC development and testing.