cctbx contributors guide

As discussed at the Gordon Research Conference for Diffraction Methods in Structural Biology, 07/30/18, the following guidelines are agreed upon for developers wishing to contribute code to cctbx:

• Cctbx is open source.
• We welcome third party contributions, but note that there is a cost for managing third party contributions.
• Cctbx is not a free-for-all.
• Contributors should be encouraged to review their plans for contributions before doing a large amount of work and submitting a pull request, but that shouldn't preclude users from submitting requests.
• Interface changes and other breaking changes should be communicated to the bulletin boards (cctbxbb@phenix-online.org for example).

Expectations for contributions

• Include documentation: docstrings for functions, in-line comments, and help strings for command line programs.
• Include tests. Testing includes unit tests (individual functions) and integration tests (full program), and possibly multiple of each with different inputs.
• Run the cctbx tests. If appropriate, run tests from other projects affected by the new code.
• Do not add external dependencies without discussion.

Expectations for developers

• We will respond to contributions, at least with "I don't have time to review this right now".
• We can deny pull requests, but if we do so, we should do so with constructive feedback, following consistent rules.
• The build meeting team will review tickets and pull requests to ensure regular feedback.

See cctbx-Developer-Guidance for more details.