NPM scripts for site CI

[chalin]

Notes:

• Added netlify-cli for serve script.
• Minimal edits done to README. More to come in the scope of another PR.
• I'm choosing to leave the Makefile for now. We can discuss this during our design meeting later today. Related: #103

Note that to use another version of Hugo, one has to npm uninstall hugo-extended.

cc @kapunahelewong

Signed-off-by: Patrice Chalin pchalin@gmail.com