[nautilus-actions/file-manager-actions] Makefile.am: add gtk-doc comment

[Pierre Wieser <pwieser src gnome org>]

commit 0696c7cf4dd3205750d025bf38dde247f2248a96
Author: Pierre Wieser <pwieser trychlos org>
Date:   Fri Sep 18 00:04:08 2015 +0200

    Makefile.am: add gtk-doc comment

 docs/reference/Makefile.am |   21 +++++++++++++++++++++
 1 files changed, 21 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/Makefile.am b/docs/reference/Makefile.am
index d34b8d7..d60f29a 100644
--- a/docs/reference/Makefile.am
+++ b/docs/reference/Makefile.am
@@ -24,6 +24,27 @@
 #   Rodrigo Moya <rodrigo gnome-db org>
 #   Pierre Wieser <pwieser trychlos org>
 #   ... and many others (see AUTHORS)
+#
+# pwi 2015- 9-17 gtk-doc
+# --enable-gtk-doc
+#   doesn't build anything if neither --enable-gtk-doc-html nor
+#   --enable-gtk-doc-pdf is set
+# --enable-gtk-doc-html
+#   is only considered if --enable-gtk-doc is also set
+#   builds html/ and xml/ subdirectories
+#   installs html/ subdir only in DESTDIR/share/gtk-doc/html/filemanager-actions-3
+#   (xml/ subdir doesn't seem to be used)
+# --enable-gtk-doc-pdf:
+#   uses gtkdoc-mkpdf
+#   requires dblatex or fop
+#   doesn't work for now (see below)
+#
+# pwi 2015- 9-17 gtk-doc-1.24-1.fc22.noarch
+# It seems that gtkdoc-mkpdf, which may use dblatex or fop, is actually
+# unable to build any pdf document as the corresponding variables are
+# unset in the script.
+# These variables are unset as if the package had been built without
+# the corresponding utilities be available on the package build system.
 
 #
 # FileManager-Actions Reference Manual