Developer guidance needs updating

[graeme-winter]

At:

https://github.com/cctbx/cctbx_project/wiki/cctbx-Developer-Guidance

Contains e.g. "Printing output

Use print >> log, bla and not print bla .

Use show function to print a summary or result of code execution instead of in-lining print statements directly into the code.

Avoid unconditional printing.'"

Which should at the very least be updated to print(bla, file=log) and from __future__ import print_function etc.