Update Readme in docs-app

[ipopescu]

Running Docusaurus in localhost is pretty easy, You have to perform the following few steps:

• Install node js
• Install yarn via npm: npm install --global yarn
• Clone the repository https://github.com/casper-network/casper-node/docs-app on your local machine
• Go to docs-app and run the following commands
• yarn install - required only once for a folder
• yarn run start - to start the local server (I have done remove '--no-open' part, so that it will automatically open the localhost page in our browser)
• Navigate to http://localhost:3000/

Remove the subtree with these commands:

• git subtree pull --prefix source https://github.com/casper-network/documentation main --squash
• git subtree push --prefix source https://github.com/casper-network/documentation main