put F-Droid and GPlay badges locally

[532910]

this adds images for F-Droid and GPlay buttons for README.md

Signed-off-by: Sergio E. Nemirowski [email protected]

Pull Request Checklist

• [ ] Changes has been tested on an Android device or Android emulator with API 16
• [ ] UI change has been tested on both light and dark themes
• [X] Pull request is based on the develop branch
• [ ] Pull request updates CHANGES.rst
• [ ] Pull request includes screenshots or videos if containing UI changes
• [X] Pull request includes a sign off

[532910]

This is based on jitsi-meet repository and fixes the current look: