Aligned "todo.sh do" usage message with existing support of passing multiple numbers.

tests/t1500-do.sh

@@ -8,7 +8,7 @@ test_description='do functionality
 
 test_todo_session 'do usage' <<EOF
 >>> todo.sh do B B
-usage: todo.sh do ITEM#
+usage: todo.sh do ITEM#[, ITEM#, ITEM#, ...]
 === 1
 EOF
 

todo.sh

@@ -765,7 +765,7 @@ case $action in
     fi;;
 
 "do" )
-    errmsg="usage: $TODO_SH do ITEM#"
+    errmsg="usage: $TODO_SH do ITEM#[, ITEM#, ITEM#, ...]"
     # shift so we get arguments to the do request
     shift;