Add documentation on GitBook

[alexrp]

We can probably move some of this to GitBook as well:

• https://github.com/vezel-dev/cathode/blob/1e6bca1155a01360e8086ec3816afe0dd6800e9f/RESOURCES.md
• https://github.com/vezel-dev/cathode/blob/1e6bca1155a01360e8086ec3816afe0dd6800e9f/README.md#terminals

[alexrp]

Started in 614b283.

[sandrock]

Hi. I am considering using this lib but there is no "getting started" documentation. I'm not sure where to start.

[alexrp]

Hi! Yeah, I need to get around to this issue at some point. 🙏 In the meantime, the best recommendation I can give is to check out the samples, as they exercise most broad-strokes functionality in the library.

If you have any questions beyond that, I always monitor the Questions discussion category and the Discord. 🙂