Merge remote-tracking branch 'origin/master'

README.md

-Installation instructions from NetData: https://github.com/firehol/netdata/wiki/Alerta-monitoring-system
-
-Other documentation sources:
-
-- http://docs.alerta.io/en/latest/index.html
-- http://alerta.io
-
-# Docker based Installation
-
-- [Extending the image for Python packages](https://github.com/alerta/docker-alerta/blob/master/Dockerfile)