Add Contributing Guide to SymbiFlow projects

[kgugala]

A contributing guide is a short document containing a description of the development process and rules of contribution to the project. It explains how to submit valuable and easy-to-understand modifications and how to create clearly defined issues.

Currently, only a few projects which constitute SymbiFlow have proper contribution guidelines. Most of them need new guidelines or have the existing ones updated. Also, the style and formatting should be unified across all guides.

The contribution guides should consist of:

• A short introduction explaining what kind of contributions are accepted.
• Code of conduct either as a link to the dedicated file or a separate description.
• Information about useful resources and communication channels
• Information about submitting changes
  • Code style
  • Information about available tests
  • Information about assigning reviewers
  • Need for the Developer Certificate of Origin
• Information about opening issues
  • How to search for available issues
  • How to navigate through the issues using project-specific labels
  • Conventions for naming issues
  • How to request an enhancement
  • How to report a bug, need for a minimal code sample, and the way of reproducing the problem.

Projects missing the contribution guide:

• sv-test
• symbiflow-docs
• symbiflow-arch-defs
• python-symbiflow-v2x
• fasm
• icestorm
• python-sdf-timing

Project that requires review of contribution guide:
-[prjxray[(https://github.com/SymbiFlow/prjxray)

Additional information could be obtained from:

• Projects README
• SymbiFlow documentation
• Official talks available on the SymbiFlow’s website