contrib guide: update ToC
contrib guide: update ToC

The table of contents has slipped out of date.

FYI I'm generating a ToC with a command like:
	pandoc -t markdown_github --toc -s README.md
and then picking up the modifications and dropping them in the document.

Not the best workflow, but..markdown.

Signed-off-by: Tim Pepper <4807564e5a18784afafcf20dbdb5591e844b9075@vmware.com>

kubernetes/community,kubernetes/community,pwittrock/community,bgrant0607/community,pwittrock/community,kubernetes/community,bgrant0607/community