building-introduction: Mention flatpaked flatpak-builder and app store

processes

Author: bbhtt

docs/building-introduction.rst

@@ -5,6 +5,12 @@ Building Introduction
 applications get built with Flatpak. This page provides an additional general
 overview of what's involved.
 
+.. note::
+
+  App stores like `Flathub <https://docs.flathub.org/docs/for-app-authors/submission>`_
+  has additional requirements on the building process. Please refer to
+  their respective documentation for details.
+
 flatpak-builder
 ---------------
 
@@ -13,6 +19,10 @@ allows you to take the source files for an application and build it into a
 Flatpak application. It also allows multiple other dependencies to be built
 at the same time, which get bundled into the build.
 
+It is packaged by several distributions and there is a
+`Flatpak package <https://flathub.org/apps/org.flatpak.Builder>`_ called
+``org.flatpak.Builder`` available for it too on Flathub.
+
 The input to ``flatpak-builder`` is a manifest file. This specifies the
 parameters for the application that will be built, such as its name and
 which runtime it will depend on. The manifest also lists all the modules