Add UI description to to use in 2013/morgan1

In other words:

    * Right : go forwards one day.
    * Left  : go backwards one day.
    * Up    : go forwards 20 days.
    * Down  : go backwards 20 days.

The try.sh script also has this detail and improves the way it tells the
user about Comets Halley and Hale-Bopp.

2013/morgan1/try.sh

@@ -15,6 +15,19 @@ make CC="$CC" all >/dev/null || exit 1
 # clear screen after compilation so that only the entry is shown
 clear
 
+echo "Usage instructions: once the program is in focus, use the arrow keys to" 1>&2
+echo "go through the dates:" 1>&2
+echo 1>&2
+echo "Right: go forwards one day." 1>&2
+echo "Left : go backwards one." 1>&2
+echo "Up   : go forwards 20 days." 1>&2
+echo "Down : go backwards 20 days." 1>&2
+echo 1>&2
+echo "Note: the third run is Comet Halley - look for 'Ha'." 1>&2
+echo 1>&2
+echo "Note: the fourth run is Comet Hale-Bopp - Look for 'Hb'." 1>&2
+echo 1>&2
+
 read -r -n 1 -p "Press any key to run: echo 1985/10/28 | ./morgan1: "
 echo 1>&2
 echo "1985/10/28" | ./morgan1
@@ -25,12 +38,16 @@ echo 1>&2
 echo "1996/12/31" | ./morgan1
 echo 1>&2
 
-read -r -n 1 -p "Press any key to run: echo 1986/03/31 | ./morgan1 # Comet Halley (look for 'Ha'): "
+echo "The next one is Comet Halley. Look for 'Ha' in the display." 1>&2
+read -r -n 1 -p "Press any key to run: echo 1986/03/31 | ./morgan1: "
 echo 1>&2
-echo "1986/03/31" | ./morgan1 # Comet Halley (look for 'Ha')
+# Comet Halley (look for 'Ha'):
+echo "1986/03/31" | ./morgan1
 echo 1>&2
 
-read -r -n 1 -p "Press any key to run: echo 1997/04/01 | ./morgan1 # Comet Hale-Bopp (look for 'Hb'): "
+echo "The next one is Comet Hale-Bopp. Look for 'Hb' in the display." 1>&2
+read -r -n 1 -p "Press any key to run: echo 1997/04/01 | ./morgan1: "
 echo 1>&2
-echo "1997/04/01" | ./morgan1 # Comet Hale-Bopp (look for 'Hb')
+# Comet Hale-Bopp (look for 'Hb'):
+echo "1997/04/01" | ./morgan1
 echo 1>&2