Improve README.md

[daiking1756]

Background

• current: "househackathon2020"
• There are no information about Kaobato

Goal

• Add bellow content
  • Usage of this app (How to play Kaobato)
  • GIF of playing Kaobato
  • Link of the material, such as GoogleSlide, YouTube demo movie, ...etc

[kugimasa]

Add gif & image