[gimp] build: stable flatpak manifest is now hosted at flathub.

[Jehan Pagès <jehanp src gnome org>]

commit dd924bb33ad1ed262b0977b0f3cbfeee6dae2c2c
Author: Jehan <jehan girinstud io>
Date:   Mon Oct 23 21:16:05 2017 +0200

    build: stable flatpak manifest is now hosted at flathub.

 build/flatpak/flatpak-howto.txt         |   16 ++++++
 build/flatpak/org.gimp.GIMP-stable.json |   77 -------------------------------
 2 files changed, 16 insertions(+), 77 deletions(-)
---
diff --git a/build/flatpak/flatpak-howto.txt b/build/flatpak/flatpak-howto.txt
index 8b73fd5..6d5ade7 100644
--- a/build/flatpak/flatpak-howto.txt
+++ b/build/flatpak/flatpak-howto.txt
@@ -1,6 +1,22 @@
 GIMP Flatpak HowTo
 ==================
 
+Stable build
+~~~~~~~~~~~~
+
+The stable manifest is maintained at flathub: https://github.com/flathub/org.gimp.GIMP
+
+Development and nightly builds
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Flathub does not host non-stable builds, therefore they are maintained
+separately on the GIMP repository. Nevertheless they should remain as
+close to the stable manifest as possible since they are meant to become
+stable too.
+
+Building and maintaining
+~~~~~~~~~~~~~~~~~~~~~~~~
+
 * Install flatpak and flatpak-builder. There are packages for most
   distributions. Check: http://flatpak.org/getting.html
   Use at least flatpak 0.9.5.