Change wording in warning to be clearer. Correct ranges on contrast

and gamma.

files/settings-default.cfg

@@ -1,5 +1,6 @@
-# WARNING: Editing this file might have no effect, as these settings
-# are overwritten by your user settings file.
+# WARNING: If this file is named settings-default.cfg, then editing
+# this file might have no effect, as these settings may be overwritten
+# by your user settings.cfg file (see docmentation for its location).
 #
 # This file provides minimal documentation for each setting, and
 # ranges of recommended values.  For detailed explanations of the
@@ -192,10 +193,10 @@ vsync = false
 # Maximum frames per second.  (1.0 to 200.0).
 framerate limit = 0.0
 
-# Game video contrast.  (0.0 to 1.0).  No effect in Linux.
+# Game video contrast.  (>0.0).  No effect in Linux.
 contrast = 1.0
 
-# Video gamma setting. (0.0 to 1.0).  No effect in Linux.
+# Video gamma setting. (>0.0).  No effect in Linux.
 gamma = 1.0
 
 [Water]