🎵 Relaxing song #9
Description
Is your feature request related to a problem? Please describe.
A relaxing song in the background can help the user.
Describe the solution you'd like
Add a song in the background when the breathing exercise begins, and add a button so the user can enable/disable it.
Describe alternatives you've considered
The user might be able to choose custom songs from local files.
Additional context
The songs should be royalty-free. Also, this issue should consider #8.