[gimp] INSTALL: add a precision about which mypaint-brushes branch to install.

[Jehan Pagès <jehanp src gnome org>]

commit fe4bbc4d9c4bbecf650163fadfc6af8e60caa219
Author: Jehan <jehan girinstud io>
Date:   Mon Jan 1 23:04:06 2018 +0100

    INSTALL: add a precision about which mypaint-brushes branch to install.

 INSTALL.in |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/INSTALL.in b/INSTALL.in
index cd94c7b..52b1cf9 100644
--- a/INSTALL.in
+++ b/INSTALL.in
@@ -89,6 +89,10 @@ header files installed.
 
         https://github.com/Jehan/mypaint-brushes
 
+     If installing from repository, install from branch "v1.3.x" or the
+     particular tag "v1.3.0". In particular do not install from master
+     which installs brushes incompatible with GIMP.
+
  11. You may want to install other third party libraries or programs
      that are needed for some of the available plug-ins. We recommend
      to check that the following libraries are installed: libjasper,