[gimp-help] build: fix make dist

[Jacob Boerema <jboerema src gnome org>]

commit 536cd6eabcb1ce52027baadf8668842555704614
Author: Jacob Boerema <jgboerema gmail com>
Date:   Thu Mar 10 18:54:43 2022 -0500

    build: fix make dist
    
    (cherry picked from commit 59bc3c4ae40846b01764d9b4f0a8672644d35270)

 Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/Makefile.am b/Makefile.am
index c48624a82..9512c66e9 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,6 +1,6 @@
 ## Process this file with automake to produce Makefile.in
 
-SUBDIRS = quickreference
+SUBDIRS = quickreference m4macros
 
 # used for creating the ChangeLog
 LAST_RELEASE_TAG = GIMP_HELP_2_8_2