Signed-off-by: NSteve Martinelli <stevemar@ca.ibm.com>

Checks-in "featured-background.jpeg" and cleans up sync.py and DEVELOPMENT.md
Add git ignores for node_modules and "generated" version-switcher.js

The DEVELOPMENT.md was very out of date! Also uncovered some difficult
to work with things along the way such as https://github.com/tektoncd/website/issues/38
which made it so that you need credentials to access the GCP bucket with
the background image in order to be able to run the sync script. I've
added a very hacky env var which lets one skip this until we tackle #38

With this commit we'll have the basic docs that are required for all
Tekton projects
(https://github.com/tektoncd/community/blob/master/process.md#project-requirements)
and a start at development + contributing guides, hopefully enough to
meet the requirements for #2 though we could still flesh these out
further.

Fixes #2