Add documentation for how to run tests

[goanpeca]

How is this normally handled? should we add an environment.yaml to set a full environment for qtpy? or should we add a specfile/requirements-test.txt file?

@ccordoba12, @Nodd?

[ccordoba12]

An environment.yaml along with some instructions in our README would be fine for me :-)

[goanpeca]

sure that would work :-)

[jitseniesen]

I just wrote http://github.com/spyder-ide/spyder/wiki/Dev%3A-Testing for the spyder repo - maybe you can use it as a starting point?

[CAM-Gerlach]

This has been changed and simplified significantly following PR #262 . I was already planning to add a Contributing Guide as following the mold of an updated, simplified and more helpful standardized version of the Spyder one, which would cover this, so I'll take care of this soon.