Add yarn and data:seed_fake steps in setup instructions to README.md

## Description of the issue below:

> - Add the new instructions in the README.md in the topic `Setting up an Environment`

>  - Step 8 run the `yarn` command

> - Step 9 run the `rails data: seed_fake` command


## Change location below:

![image](https://user-images.githubusercontent.com/18706961/110258155-da00ed00-7f7f-11eb-84ba-665acd802b36.png)

