Add Open Collective Backer information
Add Open Collective Backer information

Great news, we finally got our first backer @Datawrapper on open collective. In order to show our gratitude, I add back the backer section in the readme document. Meanwhile, if there is any expense related to contributing Hexo, like website, domain, host, and etc. You know there is a way to reimburse.  😄
hexojs/hexo,ppker/hexo,ppker/hexo,kywk/hexi,kywk/hexi,hexojs/hexo