The API usage page in the documentation should point to the Redoc page

[mfornasa]

As I first time user, I was unaware of the existence of the Redoc page https://www.opencost.io/api, as it is not linked in the documentation "API usage" page (https://www.opencost.io/docs/api). There's should be a link.

[mattray]

I've been meaning to reorganize our docs, I'll add this to my backlog.