README: Add a link to the slides
A Network Service Mesh is an extension of the Service Mesh concept common in applications to Network Services. It is part of an attempt to reimagine NFV in a Cloud-native way.
+- [Network Service Mesh Intro slides](https://docs.google.com/presentation/d/1C3r91ev0tWnFFUjiV4W84Hp965YGR1D9lChZo73Jwq0/edit#slide=id.g375263091c_1_0)
