Optimise and improve README

[Richienb]

I have made the following modifications in order to optimise and improve the README:

• Converted the HTML links to Markdown links
• Added information on how to insert the install button in Markdown
• Changed the hard to read, double underscores to double asterisks
• Changed the HTML code tag to the Markdown code tag

[NinoSkopac]

Is this repo dead? @zackbloom