docs/userguide: the correct command is 'floating enable', not 'mode floating' (Thanks Sander)

Fixes: #453

docs/userguide

@@ -437,7 +437,7 @@ for_window [criteria] command
 *Examples*:
 ------------------------------------------------
 # enable floating mode for all XTerm windows
-for_window [class="XTerm"] mode floating
+for_window [class="XTerm"] floating enable
 
 # Make all urxvts use a 1-pixel border:
 for_window [class="urxvt"] border 1pixel
@@ -445,7 +445,7 @@ for_window [class="urxvt"] border 1pixel
 # A less useful, but rather funny example:
 # makes the window floating as soon as I change
 # directory to ~/work
-for_window [title="x200: ~/work"] mode floating
+for_window [title="x200: ~/work"] floating enable
 ------------------------------------------------
 
 === Variables

src/cfgparse.y

@@ -991,7 +991,7 @@ assign:
         /* Compatibility with older versions: If the assignment target starts
          * with ~, we create the equivalent of:
          *
-         * for_window [class="foo"] mode floating
+         * for_window [class="foo"] floating enable
          */
         if (*workspace == '~') {
             workspace++;