Make instructions for setting up local instance of project clearer

[bl-aire]

While trying to set up the project locally, I had some problems so I am suggesting these improvements to make the documentation better.

• The third instruction says to "install mariadb" but it is already listed in the package.json file as a dependency and will be installed with other packages when npm i is run. I think the repetition can get contributors confused.
• On running npm run dev I got an error because I did not have nodemon installed. Stating that nodemon is a requirement for setting up the project and clearly stating how it can be installed (npm install -g nodemon) can fix this.

This is open to a review by a maintainer and if the proposed changes are approved, I would love to be assigned to this issue: