Update restrictions of supported platforms on certain endpoints

[sraver]

Description

Update of README to remove misleading restrictions.

Context

I implemented this library this weekend on a project, and while playing and learning the endpoints I needed to use I noticed that some of the docs were out of date. I had to dive into the code to make sure if there was some limitation hardcoded into the library, but it doesn't. It actually supports more than than only the ethereum platform, so I thought I could also update.