Fix typo in README
Author: Hans Ulrich Niedermann <hun@n-dimensional.de>
Committer: Tim Moore <timoore@redhat.com>
Before you can run FlightGear you will also need to download and
install the "base" package which is a collection of textures, sounds,
-sample scenery, and other data files need by the sim.
+sample scenery, and other data files needed by the sim.
For additional install help for specific platforms please browse the
"docs-mini/" subdirectory.