add custom interpolation nb

Author: chrishavlin

docs/examples.rst

@@ -13,6 +13,7 @@ Example Notebooks
     examples/example_007_interpolation
     examples/example_008_interpolation_with_refinement
     examples/example_009_custom_transformations
+    examples/example_010_custom_interpolations
 
 These notebooks demonstrate `yt_xarray` usage:
 
@@ -24,4 +25,5 @@ These notebooks demonstrate `yt_xarray` usage:
 - Example 006: :doc:`examples/example_006_yt_method_access`
 - Example 007: :doc:`examples/example_007_interpolation`
 - Example 008: :doc:`examples/example_008_interpolation_with_refinement`
-- Example 010: :doc:`examples/example_009_custom_transformations`
+- Example 009: :doc:`examples/example_009_custom_transformations`
+- Example 010: :doc:`examples/example_010_custom_interpolations`