Update install_check and readme

Author: mwcraig

README.md

@@ -6,7 +6,7 @@
 
 # Installation
 
-### Installation instructions last updated 2021-06-06
+### Installation instructions last updated 2021-06-07
 
 The code in the tutorial has been written using Python 3; many of the dependencies may not be available for Python 2.7.
 

install_check.py

@@ -19,7 +19,9 @@
     'ipydatagrid',
     'ipycytoscape',
     'ipygany',
-    'jupyterlab'
+    'jupyterlab',
+    'voila',
+    'pyvista',
 ]
 
 import_result = {p: False for p in requirements}