Fine-tune public landing page -- acartio.io/home

[scottveirs]

• [x] Change "Sighting age" to "Location age" or something else more generic so that not only visual, but also acoustic (and other sensors used to detect presence/absence) are included in the term.
• [x] Add some legend or other tool to explain the significance of the size (radius) of the markers on the map
• [x] Explain somewhere that this map shows occurrence of all marine species
• [ ] Should we explain that you can click on a marker to get more info (and then clarify what each field means, and why we are presenting UTC timestamps => e.g. this is a data cooperative from which visualizations or applications like orcamap can be created; it's not meant to be a real-time application or visualization tool itself? Maybe we need a "how to" demo to orient new users?

[scottveirs]

Created this issue in forked repo to address final checkbox, so closing.