Refactor documentation landing page and add docker development support

Docker development support

I created a Docker image to standardize builds on my computer + the gitlab pipeline, plus two helper scripts that launch the containers with good options. Instructions in the README.

Reorganized documentation landing page

Reformatted the documentation landing page at @sjerome's suggestion.

Add resources page

Fed from data/hpc-resources.yaml

Signed-off-by: Georgia Stuart gstuart@umass.edu