Improve 2019/burton/try.sh + shellcheck comments

The shellcheck comments are in cow.sh and check.sh: added the URL for
each supposed problem as per that issue.

2019/burton/try.sh

@@ -15,15 +15,19 @@ make CC="$CC" all >/dev/null || exit 1
 # clear screen after compilation so that only the entry is shown
 clear
 
-echo "$ cat prog.c" 1>&2
+read -r -n 1 -p "Press any key to show prog.c: "
+echo 1>&2
 cat prog.c
 echo 1>&2
 
 for i in prog.c Makefile README.md; do
-    echo "$ ./prog < $i && wc < $i" 1>&2
+    read -r -n 1 -p "Press any key to run: ./prog < $i && wc < $i: "
+    echo 1>&2
     printf "prog: %s\n%4s: %s\n\n" "$(./prog < "$i"|tr -s ' ')" "wc" "$(wc "$i" | tr -s ' ')"
 done
 echo 1>&2
 
-echo "$ make test" 1>&2
+read -r -n 1 -p "Press any key to run: make test: "
+echo 1>&2
 make test
+echo 1>&2