Fix GENERATE.md link broken issue and add CONTRIBUTING-CN.md for Chinese relevant contributors

- [x] Read [CONTRIBUTING.md](https://github.com/ochococo/Design-Patterns-In-Swift/blob/master/CONTRIBUTING.md]) - [x] Only edited files inside `source` folder (IMPORTANT) and commited them with a meaningful message - [x] Ran `generate-playground.sh`, no errors - [x] Opened playground, it worked fine - [x] Did not commit the changes caused by `generate-playground.sh` - [x] Linked to and/or created issue - [x] Added a description to PR --- - link update: GENERATE.md -> CONTRIBUTING.md Fix #127 - add CONTRIBUTING-CN.md: describe how to contribute to Chinese translation and relevant branch descriptions.