Improve readme

[nymann]

We need a get started section that makes it easy for new developers to set up a development environment.

This information should also be pinned in our Discord channel.

@NimishVerma do you want to help me with this? :-)

[nymann]

Use the branch issue-11-Improve_readme for working on this.

git fetch --all
git checkout issue-11-Improve_readme

[NimishVerma]

Will do

[NimishVerma]

PR #12 adds docker setup, let me know if you want me to add the local setup instruction and/or improve this one.