Pull-request checklist needs a revamp

[pp-mo]

Problems spotted :

1. "Iris tests may be run with python setup.py test " -- is this still true, or is there a bette way ?
2. "There is a python module for checking pep8 compliance: python-pep8" -- should now be referring to flake8
3. "the files ./conda-requirements.yml and ./minimal-conda-requirements.yml are used to define the software environments" -- now uses combined requirements process in iris/requirements
4. "test-images-scitools is a github project containing reference plot images" -- has moved
5. "see Graphics tests" -- docs-page still incomplete https://scitools.org.uk/iris/docs/latest/developers_guide/tests.html#graphics-tests

[rcomer]

I was rummaging in the image tests today (as you do) and noticed there seems to be an option for displaying the figures that you are testing:

iris/lib/iris/tests/__init__.py

Lines 140 to 143 in 3b4a00d

	if MPL_AVAILABLE and "-d" in sys.argv:
	sys.argv.remove("-d")
	plt.switch_backend("tkagg")
	_DISPLAY_FIGURES = True

This would be useful information to have in the proposed new How To Run the Tests section.

[tkknight]

Fixed by #3852 and other earlier PR's.