Installation.md: build dependency rsync
Installation.md: build dependency rsync

Building the Debian package requires rsync.

Signed-off-by: Heinrich Schuchardt <2cd7bb605d542f55cc27b85da62ad2c96ce31039@gmx.de>

gotthardp/lorawan-server,gotthardp/lorawan-server,gotthardp/lorawan-server