Add git command to get latest version
Add git command to get latest version

Currently our instructions for integrating from source leave the user with the latest master branch. Adding git command to check out the latest proper release.
mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone,mixpanel/mixpanel-iphone,carezone/mixpanel-iphone,carezone/mixpanel-iphone