message: Update README.md
  Add a note for gltfpack binaries
diff: @@ -282,6 +282,8 @@ cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_TOOLS=ON
  cmake --build . --config Release --target gltfpack
  ```
  +> Note: instead of building gltfpack manually, you can download a pre-built binary on [Releases page](https://github.com/zeux/meshoptimizer/releases).
  +
  You can then run the resulting command-line binary like this (run it without arguments for a list of options):
  ```
  