Tool Definition docs

[EricGustin]

After going through the docs I realized that we don't say anything about what parts of a tool definition are sent to the language model. Knowing what is sent to the model is necessary for creating great Arcade tools.

[byrro]

Good call. Occurred to me now that we'll also need to document what types are allowed and things like max length for the docstrings. We still don't have good error messages for these, so the docs are even more important.