Add a first content into the AUTHORS file

AUTHORS.md

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+A full developer contributors list can be found [here](https://github.com/vector-im/riotX-android/graphs/contributors). 
+
+# Core team:
+
+Even if we try to be able to work on all the functionalities, we have more knowledge about what we have developed ourselves.
+
+## Benoit: Android team leader
+
+[@benoit.marty:matrix.org](https://matrix.to/#/@benoit.marty:matrix.org)
+- Android team leader and project leader, Android developer, GitHub community manager.
+- Specialist of the account creation, and many other fun features.
+- Reviewing and polishing developed features, code quality manager, PRs reviewer, GitHub community manager.
+- Release manager on the Play Store
+
+## François: Software architect
+
+[@ganfra:matrix.org](https://matrix.to/#/@ganfra:matrix.org)
+- Software architect, Android developer
+- First developer on the project.
+- Work mainly on the global architecture of the project.
+- Specialist of the timeline, and lots of other features.
+
+## Valere: Product manager, Android developer
+
+[@valere35:matrix.org](https://matrix.to/#/@valere35:matrix.org)
+- Product manager, Android developer
+- Specialist on the crypto implementation.
+
+# Other contributors
+
+First of all, we thank all contributors who use RiotX and report problems on this GitHub project or via the integrated rageshake function.
+
+We do not forget all translators, for their work of translating RiotX into many languages. They are also the authors of RiotX.
+
+Feel free to add your name below, when you contribute to the project!