`neil new`: link to upstream docs for list of built in templates

[teodorlu]

Please answer the following questions and leave the below in as part of your PR.

• [ ] This PR corresponds to an issue with a clear problem statement.

  • [x] No issue, but discussed on Slack: https://clojurians.slack.com/archives/C019ZQSPYG6/p1676654582925489?thread_ts=1676645855.709469&cid=C019ZQSPYG6

• [ ] I have updated the CHANGELOG.md file with a description of the addressed issue.

Should this be merged?

This PR contains proposed helptext changes incorporating suggestions from @seancorfield. I think we could get something better if we put in a bit more time.

Alternatives

166 generates helptext to include list of built in templates.

[teodorlu]

Reporting some intermediate conclusions.

From what I can see, there's no concept of "valid built-in template" in org.corfield.new. The create function takes a template as input. Valid template symbols have a subfolder in resources/corfield/new.

Perhaps we can just peek at the classpath to get the right args? Or we could ask for the ability to answer "what are valid templates?" from deps-new's public interface.

[teodorlu]

Closing in favor of #166.