Add meaningful error message to example package

Co-authored-by: Milan Curcic <[email protected]>

Author: awvwgk

example_packages/version_file/app/main.f90

@@ -1,10 +1,10 @@
 program stub
   implicit none
-  logical :: exist
+  logical :: exists
   integer :: unit
   character(len=100) :: line
-  inquire(file="VERSION", exist=exist)
-  if (.not.exist) error stop
+  inquire(file="VERSION", exist=exists)
+  if (.not.exists) error stop "File VERSION does not exist."
   open(file="VERSION", newunit=unit)
   read(unit, '(a)') line
   close(unit)