Document CI setup in README.
Document CI setup in README.

This probably isn't the best place for it, but I don't want to put that
info on the wiki unless this branch is merged.

oshiho3/growstuff,korabh/growstuff,CloCkWeRX/growstuff,CjayBillones/growstuff,Br3nda/growstuff,GabrielSandoval/growstuff,borracciaBlu/growstuff,iressgrad15/growstuff,Growstuff/growstuff,dv2/growstuff,Growstuff/growstuff,gustavor-souza/growstuff,pozorvlak/growstuff,pozorvlak/growstuff,andrba/growstuff,sksavant/growstuff,pozorvlak/growstuff,pozorvlak/growstuff,cesy/growstuff,maco/growstuff,CloCkWeRX/growstuff,dv2/growstuff,oshiho3/growstuff,Br3nda/growstuff,borracciaBlu/growstuff,GabrielSandoval/growstuff,CarsonBills/GrowStuffCMB,borracciaBlu/growstuff,cesy/growstuff,josefdaly/growstuff,sksavant/growstuff,Br3nda/growstuff,oshiho3/growstuff,GabrielSandoval/growstuff,korabh/growstuff,CloCkWeRX/growstuff,josefdaly/growstuff,CarsonBills/GrowStuffCMB,iressgrad15/growstuff,jdanielnd/growstuff,andrba/growstuff,maco/growstuff,GabrielSandoval/growstuff,yez/growstuff,borracciaBlu/growstuff,cesy/growstuff,korabh/growstuff,korabh/growstuff,josefdaly/growstuff,gustavor-souza/growstuff,andrba/growstuff,gustavor-souza/growstuff,jdanielnd/growstuff,Growstuff/growstuff,maco/growstuff,CjayBillones/growstuff,josefdaly/growstuff,iressgrad15/growstuff,dv2/growstuff,CjayBillones/growstuff,jdanielnd/growstuff,yez/growstuff,cesy/growstuff,yez/growstuff,sksavant/growstuff,maco/growstuff,jdanielnd/growstuff,CarsonBills/GrowStuffCMB,yez/growstuff,andrba/growstuff,CarsonBills/GrowStuffCMB,gustavor-souza/growstuff,CjayBillones/growstuff,Br3nda/growstuff,sksavant/growstuff,CloCkWeRX/growstuff,Growstuff/growstuff,oshiho3/growstuff,dv2/growstuff