Add badges to README

[lnx00]

Description

This PR add 4 badges (Provided by Shields.io) at the top of the README to display the following information:

• Workflow Status (Did the gradle checks pass or fail?)
• No. of Issues
• Commit activity per week
• License

These badges allow an easy overview of the project status. They help to see if the project is actively maintained and whether it's working in it's current state.

Related Issue

N/A

Screenshots:

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.