Add information on landing page

[nathanshammah]

Request for enhancement: Show plots with benchmarks at https://qutip.org/qutip-benchmark/. Right now one sees a blank page and they could miss the benchmarks in the menu on top.

• Proposal: add plots to index page. A summary of the plots could be great.

As first step, one could include some text with commentary about the various metrics and what they mean, with hyperlinks taking to them and overall information about the benchmarks such as:

• why benchmarking qutip
• what information one can extract
• methodology of how the comparisons were chosen
• information on the CI/CD architecture
• idea: link to Xavier's journal that contains posts on the development