added various information
added various information

Mainly developer-related information, such as:
- building and testing
- godep usage
- contributing
mattcui/softlayer-go,jianqiu/softlayer-go,TheWeatherCompany/softlayer-go,maximilien/softlayer-go,maximilien/softlayer-go,mattcui/softlayer-go,TheWeatherCompany/softlayer-go,jianqiu/softlayer-go