doc: Clarify that junction sources are stored separately from project.refs

doc/source/projectconf.rst

@@ -111,7 +111,8 @@ allowed to be configured with the following values:
 
 * ``project.refs``
 
-  Source references are stored in the ``project.refs`` file.
+  Source references are stored in the ``project.refs`` file, and
+  junction source references are stored in the ``junction.refs`` file.
 
 To enable storing of source references in ``project.refs``, add the
 following to your ``project.conf``:

doc/source/projectrefs.rst

@@ -9,6 +9,9 @@ file, then it will be stored at the toplevel of your project directory
 adjacent to ``project.conf``. This can be configured in your project
 using the :ref:`ref-storage configuration <project_format_ref_storage>`
 
+Sources for :mod:`junction <elements.junction>` elements are stored
+separately in an adjacent ``junction.refs`` file of the same format.
+
 
 .. _projectrefs_basics: