Document %runvpy and better %preview doc.

docs/howtos/index.rst

@@ -9,5 +9,6 @@ things in Yuuno.
    :maxdepth: 2
 
    reuse_preview
+   run_vpy
    auto_import_yuuno
    configure_yuuno

docs/howtos/reuse_preview.rst

@@ -15,6 +15,17 @@ Step by step
 
    This should show a simple preview widget without an image.
 
+   .. important::
+
+      Make sure this code is run in its own cell as Yuuno will only save the frame when switching the clip
+      of the preview instance.
+
+   .. note::
+
+      On older IPython versions you might need to import `display` manually. Do so using::
+
+          from IPython.display import display
+
 2. Assign a clip to the preview-widget::
 
     my_preview.clip = core.std.BlankClip(color=[0,0,255])

docs/howtos/run_vpy.rst

@@ -0,0 +1,17 @@
+=================================
+Run vapoursynth scripts via Yuuno
+=================================
+
+You can run vapoursynth scripts (.vpy) using the line magic `%runvpy` with takes a path as an argument.
+
+It will return a dictionary with all outputs defined by the vpy-file so you can use it
+to encode or further modify the clip.
+
+Simple example:
+---------------
+
+Here is a simple example::
+
+    %runvpy test.vpy
+
+Upon successful execution it will return a dictionary with your outputs.