💡 Designer: better Readme generation

[breck7]

"The auto-generated Readme has a lot of wasted space, multiple lines between a section title and its content."

In general it could use a big overhaul.

[breck7]

https://github.com/treenotation/jtree/issues/120

[breck7]

Autogenerated readmes from the Grammar don't make sense.

The reason is the odds of the autogenerated readme being the best readme possible are 0%.

Hence, I'm rethinking this as instead of autogenerating a full readme, generating an "Overview" or "Cheat sheet" for a lang from a Grammar.