New unit yaml

[dr-shorthair]

See #200

[gschadow]

What is this?

[dr-shorthair]

A richer form that might be helpful for new code proposals.

@timbrisc has configured the issue tracker with three forms that just contain hints - see https://github.com/ucum-org/ucum/issues/new/choose
These options use the Markdown files here https://github.com/ucum-org/ucum/tree/main/.github/ISSUE_TEMPLATE

YAML forms are much richer.
Here's some I built elsewhere: https://github.com/FAIRvocabularies/vocabulary_maintenance/issues/new/choose
Some of the fields include validation.
It helps contributors put more structure in their proposals.

You can't see the effect of my proposal until it is merged.
@timbrisc may be able to configure GitHub so we can preview my suggestion, and beat it into shape.

[keilw]

This doesn't replace the XML files like ucum-essence.xml, does it?