doc/: Do not mention explicit key bindings

Since we exported help texts into text files, we are no longer able to
refer to the user's key bindings. Drop key binding references from the
online help texts.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

doc/add.txt

@@ -2,7 +2,7 @@ Add
 ===
 
 Add an item in either the TODO or Appointment list, depending on which panel is
-selected when you press 'a'.
+selected.
 
 To enter a new item in the TODO list, you will need first to enter the
 description of this new item. Then you will be asked to specify the todo
@@ -10,10 +10,9 @@ priority. This priority is represented by a number going from 9 for the lowest
 priority, to 1 for the highest one. It is still possible to change the item
 priority afterwards, by using the '+' and '-' keys inside the todo panel.
 
-If the APPOINTMENT panel is selected while pressing 'a', you will be able to
-enter either a new appointment or a new all-day long event.  To enter a new
-event, press [ENTER] instead of the item start time, and just fill in the event
-description.
+If the APPOINTMENT panel is selected, you will be able to enter either a new
+appointment or a new all-day long event.  To enter a new event, press [ENTER]
+instead of the item start time, and just fill in the event description.
 
 To enter a new appointment to be added in the APPOINTMENT list, you will need
 to enter successively the time at which the appointment begins, the appointment
@@ -21,7 +20,7 @@ length (either by specifying the end time in [hh:mm] or the duration in
 [+hh:mm], [+xxdxxhxxm] or [+mm] format), and the description of the event.
 
 The day at which occurs the event or appointment is the day currently selected
-in the calendar, so you need to move to the desired day before pressing 'a'.
+in the calendar, so you need to move to the desired day before.
 
 Notes
 -----