Initial commit

- Circle, horizontal, and vertical logos, in EPS.
- A description of the company targetting startups.
- An overview.
Logo and Description improvements

* Add png versions of logos and organize them
* Add logo guidelines and documentation
* Link the description file and add more info

https://trello.com/c/Blz5WzPA/15-update-presskit-and-communicate-its-purpose-and-existence-to-thoughtbot-team
Introduce revised logo

- Replace all logo files
- Edit readme to reflect changes
- Edit naming of files in logo readme
- Use "default/alternative" language instead of "light/dark"
- Be more explicit about when to use default vs. alt versions
Change Logos section to "Brand Assets & Guidelines" and point to new brand guide
Link Brand Guide to thoughtbot.github.io/presskit