update docs with new plugin install variable
update docs with new plugin install variable

hit0907/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,BasqueVoIPMafia/cordova-plugin-iosrtc,eface2face/cordova-plugin-iosrtc,BasqueVoIPMafia/cordova-plugin-iosrtc,hit0907/cordova-plugin-iosrtc,BasqueVoIPMafia/cordova-plugin-iosrtc,hit0907/cordova-plugin-iosrtc