Create a readme file

Create a readme file to explain others:

• what this repository is about;
• what prerequisites are needed to be set up in our workstation;
• how to do (developer) things in this project.
  • only include things that are set up in this project until this point. For example, if we haven't set up any linter (to verify code style), don't put its commands here (yet).

Use https://gitlab.com/kelassoftwareengineer/week2/qornanali_todolistapp as a good example for this.

This should be done after #1 (closed), but you may do this after #3.