[gimp] build: updates to the flatpak howto.

[Jehan Pagès <jehanp src gnome org>]

commit 8b3f5e87d825d435b5efb5ee233a7db81496d802
Author: Jehan <jehan girinstud io>
Date:   Wed Jun 7 16:53:00 2017 +0200

    build: updates to the flatpak howto.

 build/flatpak/flatpak-howto.txt |   13 +++++++++----
 1 files changed, 9 insertions(+), 4 deletions(-)
---
diff --git a/build/flatpak/flatpak-howto.txt b/build/flatpak/flatpak-howto.txt
index d071283..9e51b40 100644
--- a/build/flatpak/flatpak-howto.txt
+++ b/build/flatpak/flatpak-howto.txt
@@ -47,6 +47,10 @@ Or simply update them:
   Other than by trial and error, you can find the installed dependencies
   by running:
 
+> flatpak run --devel --command=bash org.gnome.Sdk//3.24
+
+Or if you already have a build:
+
> flatpak run --devel --command=bash org.gimp.GIMP
 
   GIMP manifest available at:
@@ -74,11 +78,12 @@ Or simply update them:
> flatpak-builder --arch=x86_64 gimp-flatpak-build-x86-64 org.gimp.GIMP.json
> flatpak-builder --arch=i386 gimp-flatpak-build-i386 org.gimp.GIMP.json
 
-  Note: if you ever want to check the `config.log` of any of the module,
-  this is available in a hidden directory of your working path.
+  Note: if you ever want to check the `config.log` of any of the module which
+  failed to compile, it is available in a hidden directory of your working path.
   For instance GIMP build dir will be `.flatpak-builder/build/gimp-1/`.
-  The number will be incrementing at each build (`flatpak-builder`
-  apparently caches every build).
+  The number will be incrementing at each build.
+  If you want to check build directories even if the builds are successful, add
+  `--keep-build-dirs` option to your command.
 
   If it ends successfuly, this will have built GIMP in new folders,
   `gimp-flatpak-build-x86-64/` and `gimp-flatpak-build-i386/`