minor typo

Signed-off-by: Isaac (.ike) Levy <ike@blackskyresearch.net>
(cherry picked from commit 5489e8ec)

README.md

 OPNsense GUI and system management
 ==================================
 
-The OPNsense project invites developers to startcontributing to
+The OPNsense project invites developers to start contributing to
 the code base.  For your own purpose or even better to join us in
 creating the best open source firewall available.