Conflict merge in Yu Sun's course notes repository with Sijia Fang

[SebastianYuSun]

• Commit: d5a3e8b
• Joint work with @SijiaFang
• I'm so happy to learn how to merge conflict with collaborators, and I realized it's quite useful and efficient. But also I want to do some further trials to see, if some collaborators made some mistakes in multiple commits by deleting some files/or datas, and the collaborators didn't realized that, how to pick up all the correct parts for all later commits and merge them back to the master path.
• Wish you all enjoy the mid-autumn festival and Chinese National Day! @cecileane @tzuhsianghung @SijiaFang