A collection of dubbo docs

• Dubbo user manual(English) or Dubbo用户手册(中文) - Describe how to use Dubbo and all features of Dubbo concretely.
• Dubbo developer guide(English) or Dubbo开发手册(中文) - Detailly introduce the design principal, extension mechanisms, code conventions, version control and building project, etc.
• Dubbo admin manual(English) or Dubbo管理手册(中文) - Describe how to use Dubbo registry and admin-console.