Update documentations

[SusBhh]

Description

Updated README file

• I updated the README file to include the new features in the app that were not documented and linked the list of features to the corresponding section in the file.

Update CONTRIBUTING file

• I added a more detailed description of how to build and run the app as a developer.

Fixes #(issue)

Type of change

Just put an x in the [] which are valid.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

• ./gradlew assembleDebug assembleRelease
• ./gradlew checkstyle

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

[codeclimate]

Code Climate has analyzed commit 7663afe and detected 0 issues on this pull request.

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