Tracking issue: Update setup/runner instructions

[dtig]

Removing TODOs from the landing page, and tracking them here:

• Add instructions for running a workload in the browser
• Add details about metrics and how to understand them
• Add a screenshot of the runner, update the logo

[rmahdav]

• Add instructions for running a workload in the browser: this was probably a leftover comment. The instructions has been already added for running the whole benchmark or standalone workloads.
• Add a screenshot of the runner, update the logo: the logo has been updated. I left it unchecked to add the screenshot.