Added Troubleshooting guidelines, Contribution guidelines, and Installation guidelines to README and CONTRIBUTION files

[SufiaRashid]

1. Added a contribution guide for new users looking to make their first edits to this repository. It might be confusing for them to figure out how to go about making the edits and cloning the repository in the correct way without a guide written out for them.
2. Added an installation guide for those not very equipped with technological skills. Many people might not understand how to go about downloading the app on their device or through F-DROID, which is less commonly known.
3. Adding Troubleshooting guide for in app problems related to clock not running when phone is closed or timer stopping when when is closed.

[inson1]

@SufiaRashid SMT apps were sold to ad company. Fork is here https://github.com/FossifyOrg