add F-Droid update README file
add F-Droid update README file

Signed-off-by: Jakub Sokołowski <1d3764b91b902f6b45836e2498da81fe35caf6d6@status.im>
Signed-off-by: Andrea Maria Piana <39e16ece3c2d27e1889178b15ddb376e524032f8@gmail.com>

status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react