[gimp] build: add more help text to the windows-installer-langs test.

[Jehan <jehanp src gnome org>]

commit 4055ac95e6fe8e978fc09368704e07febd44451b
Author: Jehan <jehan girinstud io>
Date:   Fri Oct 1 21:48:49 2021 +0200

    build: add more help text to the windows-installer-langs test.
    
    I always have to search again the InnoSetup repository for the language
    file. Add the link in the failed test output so that we don't waste time
    searching the next time.
    
    Also when the new lang is "Unofficial", the installer script has to be
    updated as well, because these lang files must be downloaded. Add a help
    text saying this as well.

 build/windows/installer/lang/test-installer-langs.sh | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/build/windows/installer/lang/test-installer-langs.sh 
b/build/windows/installer/lang/test-installer-langs.sh
index 01c4ca0549..2b28984661 100755
--- a/build/windows/installer/lang/test-installer-langs.sh
+++ b/build/windows/installer/lang/test-installer-langs.sh
@@ -18,6 +18,9 @@ if [ "$PO_LANGS" != "$INSTALLER_LANGS" ]; then
   echo "- PO languages:        $PO_LANGS"
   echo "- Installer languages: $INSTALLER_LANGS"
   echo "Please verify: build/windows/installer/gimp3264.iss"
+  echo "Base language files can be found in: https://github.com/jrsoftware/issrc/tree/main/Files/Languages";
+  echo "If a new language is in Unofficial/, also edit/download it from:"
+  echo "build/windows/gitlab-ci/installer-gimp-msys2.sh"
   exit 1
 fi