add upgrade message about verification issue

grub.install

@@ -6,12 +6,23 @@ post_upgrade() {
   if [ ! -f /boot/grub/grub.cfg -a -f /boot/grub/grub.cfg.pacsave ]; then
     mv /boot/grub/grub.cfg.pacsave /boot/grub/grub.cfg
   fi
-}
 
-post_install() {
+  # https://md.archlinux.org/F1JuYj5xQtWyhvH8_ilErg#
-  cat << 'EOM'
+  cat <<EOM
-Generate your bootloader configuration with:
+:: Recent versions of grub may fail to boot with secure boot enabled. The
-  grub-mkconfig -o /boot/grub/grub.cfg
+   message will look like this:
+    > error: verification requested but nobody cares:
+    > (hd0,gpt2)/grub/x86_64-efi/normal.mod
+    > Entering rescue mode...
+   Handle installation to UEFI with care and be prepared!
+   For details see: https://md.archlinux.org/F1JuYj5xQtWyhvH8_ilErg#
+EOM
+}
+
+post_install() {
+  cat <<EOM
+:: Generate your bootloader configuration with:
+     grub-mkconfig -o /boot/grub/grub.cfg
 EOM
 }