Add comprehensive release process documentation

[vhaasteren]

Summary

This PR adds detailed documentation for the PTMCMCSampler release process, which was previously undocumented and relied on institutional knowledge.

Changes Made

• Added RELEASE.md: Comprehensive release documentation including:
  • Step-by-step release process (GitHub release + conda feedstock update)
  • Prerequisites and troubleshooting information
  • Release checklist and example commands
  • Explanation of setuptools_scm version management
• Updated README.md: Added "For Maintainers" section with link to release documentation

Release Process Documented

• Manual GitHub release creation (triggers automated PyPI upload)
• Manual conda feedstock updates in conda-forge repository
• Version management via setuptools_scm (automatic from git tags)
• Troubleshooting for common issues

Benefits

• Clear, documented process for all maintainers
• Reduced dependency on specific individuals
• Consistent release procedures
• Easier onboarding of new maintainers

[kdolum]

Looks fine to me, but the proof of the pudding is in going through the steps as if you didn't know what you were doing and seeing that everything works. Also in #61 you propose to change the way that this works, so do you want to wait until that is done and update this documentation?

[vhaasteren]

Thanks! And that is exactly what I am doing right now. If it all works I'll push my updates to this branch. I have some already, so don't merge until it is all there

[vhaasteren]

@kdolum

I think that #61 is separate, and can wait. That's more work. I did just verify the current release process works (just did it), and I updated the feedstock and main repositories. I think this PR (#60) is now ready and verified.

[AaronDJohnson]

Looks good to me.