[gimp] INSTALL: add some recommended dependencies to GEGL.

[Jehan <jehanp src gnome org>]

commit 530a2bd9a52f4b7c910003ad4fa9344f7f9c020b
Author: Jehan <jehan girinstud io>
Date:   Wed Jul 18 13:12:27 2018 +0200

    INSTALL: add some recommended dependencies to GEGL.
    
    This is a "for info" comment so that packagers don't forget them when we
    sometimes depend on some specific GEGL dependencies.

 INSTALL.in | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/INSTALL.in b/INSTALL.in
index aed7117857..0b5b6a6419 100644
--- a/INSTALL.in
+++ b/INSTALL.in
@@ -45,6 +45,10 @@ header files installed.
        https://gitlab.gnome.org/GNOME/babl.git
        https://gitlab.gnome.org/GNOME/gegl.git
 
+     Note: install GEGL with libumfpack (SuiteSparse) for alternative Matting
+     engine "gegl:matting-levin" and OpenEXR library for OpenEXR format
+     support.
+
   4. You need to have installed GTK+ version @GTK_REQUIRED_VERSION@ or newer.
      GIMP also needs a recent version of GLib (>= @GLIB_REQUIRED_VERSION@), GDK-Pixbuf
      (>= @GDK_PIXBUF_REQUIRED_VERSION@), and Pango (>= @PANGOCAIRO_REQUIRED_VERSION@). Sources for these can 
be grabbed