(section{Structure Editing}): Document checkbox

toggling.

etc/orgcard.tex

@@ -1,5 +1,5 @@
 % Reference Card for Org Mode
-\def\orgversionnumber{4.40}
+\def\orgversionnumber{4.41}
 \def\year{2006}
 %
 %**start of header
@@ -297,7 +297,9 @@ are preserved on all copies.
 \section{Structure Editing}
 
 \key{insert new heading/item at current level}{M-RET}
-\key{insert new TODO entry}{M-S-RET}
+\key{insert new TODO entry/checkbox item}{M-S-RET}
+\key{toggle checkbox(es) in region/entry/at point}{C-c C-x C-b}
+\key{toggle checkbox at point}{C-c C-c}
 
 \key{promote current heading up one level}{M-LEFT}
 \key{demote current heading down one level}{M-RIGHT}