Added missing installation note for econnman.config

Summary:
econnman.config must be writeble for group owners, so change
modus accordingly.

Test Plan:
Installation of econnman.config with and without changing
file acces rights and trying to connect to ieee8021x secured network.

Reviewers: leif

CC: FillFeile

Differential Revision: https://phab.enlightenment.org/D476

README

@@ -37,6 +37,7 @@ Install::
 
         make install
         chown root:users /var/lib/connman/econnman.config
+        chmod g+w /var/lib/connman/econnman.config
 
 If you wish to install at alternative locations, then make sure to
 configure your PYTHONPATH to be able to access this location!