Blog post for running ofc-bootstrap for many clusters

Add a post for showing how to manage multiple clusters using
ofc-bootstrap and the `overrides files` feature.

Edits for context, to remove negative language and to include
additional diagrams / call to action.

Signed-off-by: Alistair Hey <alistair@heyal.co.uk>
Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

Author: Waterdrips