Consolidate Contributing vs Developer docs

[lowell80]

There seems to be much overlap between these two docs:

• https://ksconf.readthedocs.io/en/latest/contrib.html
• https://ksconf.readthedocs.io/en/latest/devel.html

I think originally there was a decent reason to keep them seperate, but at this point they need to be reviewed again. There needs to be (1) a clear line between these, and (2) cross linking where appropriate. This is currently confusing.