Partially addresses #1241
### Changes
- Adds Browsertrix logo to readme
- It detects if you're in light or dark mode and adjusts the text color
accordingly! _The future is now!_
- Minor readme updates
- Updates icon and adds favicon SVGs to the docs
- This does not yet use Konsole for the docs site title. Will have to
sort this out later along with private hosting for that font.
- Updates docs theme to use new brand colours — picked the green for
this one, will probably be consistent across all of Webrecorder's MKDocs
sites.
* Minor style updates
- Uses the Material `teal` colour which seems to be a close match... This will be changed later once I do more branding things with a proper theme override
- Adds a monochrome version of the current Browsertrix Cloud logo.
- Fixes typo :P
