Include installation of 'grunt-cli' in BUILDING.md
Include installation of 'grunt-cli' in BUILDING.md

dpocock/JsSIP,onsip/SIP.js,tqcenglish/JsSIP,voxbone/JsSIP,Escaux/SIP.js,markandrus/SIP.js,vconsult/JsSIP,CodeYellowBV/JsSIP,onsip/SIP.js,rusekr/JsSIP,josephfrazier/SIP.js,ronlobo/SIP.js,joseph-onsip/SIP.js,AaronZhangL/JsSIP,Voiceworks/SIP.js,DrumTechnologiesLtd/JsSIP