[ruby]devdocs windows setup

1. can't find gem bundler (>= 0.a) with executable bundle:
   gem install bundler -v 1.16.1
2. Unable to load the EventMachine C extension:

   gem uninstall eventmachine
   gem install eventmachine --platform ruby
   

3. LoadError: Could not open library 'libcurl':
   下载curl，并将curl/bin文件移动到ruby/bin下，如有必要的话需要修改.dll的文件名(libcurl-x64.dll -> libcurl.dll)