Updated README.md
Updated README.md

- Replaced CircleCI status badge with Azure Pipelines badge.
- Updated URLs to use https.

Signed-off-by: Peter Cucka <3f86acc50981dd0f5a25aaa62c7932429d68796e@dreamworks.com>

dreamworksanimation/openvdb,dreamworksanimation/openvdb,dreamworksanimation/openvdb,dreamworksanimation/openvdb