Add release instructions to RELEASE.md

Document release process and steps for building and uploading wheels.

Author: govindchari

RELEASE.md

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+# Release
+
+1. Update git hash in CMakeLists.txt to point to the correct version of `qoco`
+2. Update version number in `pyproject.toml` and `backend/cuda/pyproject.toml`
+3. Run `./build_cuda_wheels.sh` to build `qoco-cuda` wheels
+4. Download `qoco` wheels from `Build Wheels` workflow in `Actions` tab
+5. Upload both wheels to `pypi`