[gimp] INSTALL: add information about GEGL options to enable for the…

[Jehan <jehanp src gnome org>]

commit 9ca18c37cd415a07f869485629c7f88197ef6486
Author: Jehan <jehan girinstud io>
Date:   Tue Nov 24 22:07:26 2020 +0100

    INSTALL: add information about GEGL options to enable for the…
    
    … experimental tool "Paint Select".

 INSTALL.in | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/INSTALL.in b/INSTALL.in
index c89ae7b10b..31e784360b 100644
--- a/INSTALL.in
+++ b/INSTALL.in
@@ -48,9 +48,15 @@ header files installed.
      GEGL must be built with Cairo support, i.e. -Dcairo=enabled option (required
      for some mandatory operations such as "gegl:npd").
 
-     Optional: build GEGL with libumfpack (SuiteSparse) (`-Dumfpack=enabled`)
-     for alternative Matting engine "gegl:matting-levin" and OpenEXR library
-     (`-Dopenexr=enabled`) for OpenEXR format support.
+     Optional:
+
+     - build GEGL with libumfpack (SuiteSparse) (`-Dumfpack=enabled`)
+       for alternative Matting engine "gegl:matting-levin" and OpenEXR
+       library (`-Dopenexr=enabled`) for OpenEXR format support.
+     - build GEGL with maxflow (https://github.com/gerddie/maxflow) and
+       the option -Dworkshop=true in order to be able to select the
+       experimental Paint Select tool in the Playground (operation
+       "gegl:paint-select" is needed).
 
   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