Document test-running process in CONTRIBUTING.md
Document test-running process in CONTRIBUTING.md

pozorvlak/growstuff,yez/growstuff,cesy/growstuff,pozorvlak/growstuff,Growstuff/growstuff,pozorvlak/growstuff,yez/growstuff,cesy/growstuff,cesy/growstuff,Br3nda/growstuff,dv2/growstuff,Growstuff/growstuff,cesy/growstuff,yez/growstuff,Br3nda/growstuff,yez/growstuff,dv2/growstuff,dv2/growstuff,pozorvlak/growstuff,Br3nda/growstuff,Growstuff/growstuff,dv2/growstuff,Growstuff/growstuff,Br3nda/growstuff