Adding line about PureOS Store, remove the mention of third party.

Apps/Packaging_Apps/index.rst

@@ -7,8 +7,10 @@ Applications on the Librem 5 are supplied in two different package formats:
 
 #. Debian packages are provided as part of the `PureOS`_ operating system
    running on the phone. Core applications are provided in this format.
-#. Flatpaks are created using the Flatpak suite of tools. Third party
-   applications are provided in this format.
+#. Flatpaks are created using the Flatpak suite of tools.
+
+Purism provides the PureOS Store for users to browse and install
+applications in both formats.
 
 The following sections describe how to create packages in each format.