Replace Strapi Readme boilerplate with instructions specific to our repo

[madcalf]

The current Readme contains the Strapi boilerplate documentation and doesn't really document how to set up and develop on our specific repo.

Proposed solution:

• Add clone and yarn install steps to the beginning, which are the very first things needed to run our API

• Since we are using yarn as our package manager, remove the npm instructions, which may cause conflicts when mixed with yarn.

• Add instructions to set up the .env file with the required keys.
  (Note: these instructions are currently included in PR doc: add gitpod setup to the readme #55, but I think they're better located outside of the gitpod section since they apply to local setup as well.)

• Remove the Deployment section, which is more Strapi boilerplate that doesn't offer any useful information for our project.

• Remove or rename the Learn more and Community sections. These are also Strapi specific so anyone seeking info about our API might be disappointed to arrive at the Strapi docs and community.

  • If we want to keep these links to Strapi docs, perhaps we rename those sections so it is clear what they're getting. (E.g. Strapi Resources or Learn more about Strapi and Strapi Community.)