Update documentation [Readme file]

[wandergithub]

• [x] Add Kanban Board link
• [x] Add Contributing steps and rules: (Self-assign an issue, Use Kanban Board, Fork, Ask for a review on a PR)
• [x] Add a purpose section to describe the main purpose of the app, it being a place to develop everyone's React.js skills in a collaborative environment. As you get familiar with the app you can showcase the app in your personal portfolio or talk about your contribution while looking for jobs.
• [x] Add a section to display other interesting projects on which people can collaborate on.