Update OpenZeppelin template documentation (#5398)

# Description
Updates `template.rs` to reflect the two OZ templates available and a
short description

# Checklist

* [x] My PR includes a detailed description as outlined in the
"Description" and its two subsections above.
* [x] My PR follows the [labeling requirements](CONTRIBUTING.md#Process)
of this project (at minimum one label for `T`
  required)
* External contributors: ask maintainers to put the right label on your
PR.
* [x] I have made corresponding changes to the documentation (if
applicable)

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Co-authored-by: Kian Paimani <[email protected]>
Co-authored-by: Shawn Tabrizi <[email protected]>