Add links to available example imports to resolve #809

Unavailable imports:
- import_export.rst: example.3mf (produced earlier)
- build_line.rst: club.svg

docs/examples_1.rst

@@ -122,6 +122,9 @@ Benchy
 The Benchy examples shows how to import a STL model as a `Solid` object with the class `Mesher` and
 modify it by replacing chimney with a BREP version.
 
+- Benchy STL model: :download:`low_poly_benchy.stl <../examples/low_poly_benchy.stl>`
+
+
 .. note
 
      *Attribution:*

docs/tutorial_joints.rst

@@ -185,6 +185,8 @@ Step 6: Import a Screw and bind a Joint to it
 :class:`~topology.Joint`'s can be bound to simple objects the a :class:`~topology.Compound` imported - in this case a
 screw.
 
+- screw STEP model: :download:`M6-1x12-countersunk-screw.step <M6-1x12-countersunk-screw.step>`
+
 .. image:: assets/tutorial_joint_m6_screw.svg
     :align: center