Clarify GPU contribution expectations and normalize Colab/tutorial repo references

[Copilot]

The issue asked how to contribute a combined set of gpu_process.pyx enhancements safely, what validation should be expected, and whether public function names/arguments can change. This PR tightens contributor guidance around those points and fixes stale tutorial/docs references that were still pointing to a fork.

• Contributor guidance for multi-change GPU PRs

  • Added a focused section in openpiv/docs/src/developers.rst describing how to submit related GPU enhancements in one PR.
  • Documented expected validation coverage for GPU work (CUDA/Colab execution and GPU test scope).
  • Added API compatibility guidance: avoid breaking public signatures; use compatibility wrappers/aliases when renames are necessary.

• Repository/path consistency for Colab and tutorials

  • Updated README.md Colab links to use OpenPIV/openpiv-python-gpu.
  • Updated both GPU tutorial notebooks to replace fork-based install/data links with canonical OpenPIV repository references.

• Developer onboarding correction

  • Updated developer clone instructions to point to the GPU repository used by this project.

# before (fork-specific)
pip install git+https://github.com/ericyang125/openpiv-python-gpu.git

# after (canonical)
pip install git+https://github.com/OpenPIV/openpiv-python-gpu.git

[Copilot]

Pull request overview

Updates contributor/developer documentation and tutorial/Colab references to consistently point to the canonical OpenPIV/openpiv-python-gpu repository, and adds guidance for bundling/validating larger GPU-related PRs.

Changes:

• Updated README Colab tutorial links to reference the OpenPIV/openpiv-python-gpu repo.
• Updated both GPU tutorial notebooks to replace fork-based install/data links with canonical OpenPIV references.
• Updated developers.rst with corrected clone instructions and added a “Submitting larger GPU changes” section describing expected validation and API-compat guidance.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
README.md	Normalizes Colab tutorial links to the canonical OpenPIV/openpiv-python-gpu repository.
openpiv/tutorials/openpiv_python_gpu_tutorial_basic.ipynb	Updates Colab badge/install/data links from a fork to the canonical repo.
openpiv/tutorials/openpiv_python_gpu_tutorial_advanced.ipynb	Updates Colab badge/install references from a fork to the canonical repo.
openpiv/docs/src/developers.rst	Corrects clone instructions and documents expectations for larger GPU PR submission/validation and API compatibility.

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[alexlib]

@copilot apply changes based on this feedback