Update documentation + list of associated tools

[lauralindzey]

This has been on my mental TODO list for quite some time, so adding it to where Github can also nag me =)

• Right now, the top-level README isn't bad, but I'd like it to include more of a sales-pitch of relevant tools + datasets.
• Take another pass on the marine_acoustic_msgs README. It's heavily design-focused; a lot of that could move to a HISTORY.md, and have the main README be more practitioner-focused.
• Not sure if it's worth fixing, but all of our images have a transparent background and do not display well in dark mode

[lauralindzey]

note to self: I stumbled over this imagemagick blog post (https://zck.org/imagemagick-tricks), and changing from transparent to white background looks pretty easy.