Automatically generated directory structure references for this repository

[thehowl]

From discussion in #2321.

Mhh, I think we should have here something like this: https://pkg.go.dev/std

Automatically generated, using a one-line explanation directly from the package-level godoc; collapsible or using visual hiearchy to distinguish directories. [...]

We have a workflow that checks that running go generate creates no diffs in the repository, which we can use to make sure that with each PR the README's stay in sync. [...]

So, my suggestion is to make a tool that when invoked, gets a recursive list of packages and their related one-liner documentation, and then replaces content in a markdown file to have that structure. I'll close this PR and make this as an issue, as it is different from what you're doing here; you're welcome to take it up.

Looking for something we can use to help write the README's in gnovm/, tm2/ and gno.land/, with something like this:

* [cmd](./cmd)
  * [cmd/gno](./cmd/gno) - Command gno ...
* [pkg](./pkg)
  * [pkg/doc](./pkg/doc) - Package doc implements support for documentation of Gno packages and realms ...
  * [pkg/gnoenv](./pkg/gnoenv) - Package gnoenv ...

The purpose is to aid newcomers to the project better have a glance of all the packages involved; ie. the "architecture" of the project.