doc: added documentation for available npm run scripts (#489)
doc: added documentation for available npm run scripts (#489)

with the availability of `npm run lint` there is a need for some documentation. As other useful scripts like `test:watch` are being added, I think making a small subsection about them is good
probot/probot,bkeepers/PRobot,probot/probot,bkeepers/PRobot,probot/probot