Update OSX readme

cmake/apple/readme.txt

@@ -5,12 +5,15 @@ Solarus is licensed under GNU General Public License v3.
 This OSX package contains:
 - Solarus (Solarus.app): A GUI that allows you to run a Solarus quest and
   choose your audio and video settings.
-- Solarus-run (Solarus-run.app): An executable file that directly runs
+- Solarus-run (Solarus-run.app): An application that directly runs
   a Solarus quest.
-  Run it with the path of your quest as argument
-  (the directory containing data/ or data.solarus or data.solarus.zip).
+  Normally opened, it runs the quest (the data/ folder or data.solarus or
+  data.solarus.zip) placed in the same directory than the app.
+  Through the command-line, run Solarus.app/Contents/Resources/solarus-run
+  with the path of your quest as argument (the directory containing data/
+  or data.solarus or data.solarus.zip).
   Without this argument, the current directory is used as quest path.
-  Try also 'solarus -help' to show information about the command-line
+  Try also 'solarus-run -help' to show information about the command-line
   options.
 - A sample quest. This is a very minimalist example of game with only one map
   and almost nothing to do, but you can run it or edit it.
@@ -22,4 +25,3 @@ See our website www.solarus-games.org for more information, to get help or to
 download our games or the source code of the engine.
 
 Enjoy!
-