Added dependency to the Docs

These dependencies are needed to use the plugins that are installed
as part of this guild.

As the dependencies added are not dependencies of the core package
they have been added to a separate section.

The lzip package is needed to build gnome.
https://wiki.gnome.org/Newcomers/BuildSystemComponent

doc/source/install_linux_distro.rst

@@ -73,6 +73,11 @@ At this point you should be able to get the system requirements with::
   sudo apt-get install -t stretch-backports \
       gir1.2-ostree-1.0 ostree
 
+Buildstream has a number of plugins that are installed by default which
+depend on the system packages::
+
+  sudo apt-get install \
+      lzip git bzr patch python3-arpy
 
 Buster or Sid
 ^^^^^^^^^^^^^