[gimp] devel-docs: small update for GEGL buffer leak debugging.

[Jehan <jehanp src gnome org>]

commit b9de1076ed32a692f06801f677f85b2e9ec1aa5e
Author: Jehan <jehan girinstud io>
Date:   Sun Nov 4 11:11:25 2018 +0100

    devel-docs: small update for GEGL buffer leak debugging.

 devel-docs/debugging-tips.txt | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/devel-docs/debugging-tips.txt b/devel-docs/debugging-tips.txt
index 029a3f4583..63957dea60 100644
--- a/devel-docs/debugging-tips.txt
+++ b/devel-docs/debugging-tips.txt
@@ -67,8 +67,9 @@ You may encounter this kind of warning upon exiting GIMP:
 
> EEEEeEeek! 2 GeglBuffers leaked
 
-To debug GeglBuffer leaks, set the environment variable GEGL_DEBUG to
-"buffer-alloc".
+To debug GeglBuffer leaks, make sure you built GEGL with --enable-debug
+and set the environment variable GEGL_DEBUG to "buffer-alloc".
+Your system also needs to have the header "execinfo.h".
 
 ## Debugging babl ##