[gnome-builder] doc: add note about flatpak-builder

[Christian Hergert <chergert src gnome org>]

commit cb7c05286783316773c4f72cd499164eac260289
Author: Christian Hergert <chergert redhat com>
Date:   Wed Mar 1 19:17:04 2017 -0800

    doc: add note about flatpak-builder

 doc/installation.rst |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/doc/installation.rst b/doc/installation.rst
index 1fc0072..f3f05f4 100644
--- a/doc/installation.rst
+++ b/doc/installation.rst
@@ -27,6 +27,8 @@ If Software_ does not automatically open, try opening the Stable_ flatpakref fro
 
 If you want to track Builder development, you might want our Nightly_ channel instead of Stable_.
 
+.. note:: To build flatpak-based applications, ensure that the ``flatpak-builder`` program is installed. On 
Fedora, this is the ``flatpak-builder`` package.
+
 Command Line
 ^^^^^^^^^^^^