Use igwn-mkdocs-material-theme for documentation
This MR updates the documentation build to use igwn-mkdocs-material-theme - this will mean that this site matches the look-and-feel of the main IGWN Computing Guide by default (and design).
This MR updates the documentation build to use igwn-mkdocs-material-theme - this will mean that this site matches the look-and-feel of the main IGWN Computing Guide by default (and design).