Add tip about keyboard navigation between tabs. Feel free to change the wording

or add more sentences to this rather short tip. I just didn't want to forget it right now.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@14644 57a11ea4-9604-0410-9ed3-97b8803252fd

doc/tip_of_the_day.list.in

@@ -57,6 +57,9 @@ Accounts -> Open Subaccounts from the menu.")
 decrement the selected date. You can use '+' and '-' to increment and \
 decrement check numbers as well.")
 
+ N_( "To switch between multiple tabs in the main window, press \
+Control+Alt+Page Up/Down.")
+
  N_( "In the reconcile window, you can press the spacebar to mark \
 transactions as reconciled.  You can also press Tab and Shift-Tab to \
 move between deposits and withdrawals.")