Adding demo notebook (#13)

Adding demo notebook

Author: wolfv

environment.yml

@@ -0,0 +1,14 @@
+name: xtensor-io
+channels:
+  - nodefaults
+  - QuantStack
+  - conda-forge
+dependencies:
+  - xtensor
+  - boost ==1.65.1
+  - boost-cpp ==1.65.1
+  - widgetsnbextension
+  - xtensor-io
+  - xeus-cling
+  - xwidgets
+  - notebook