Add some basic usage documentation to the README

[bbatsov]

We should probably add a least a couple of sections regarding the high-level usage of orchard and the goals of the project.

[MalloZup]

autogenerated with https://github.com/MalloZup/doghub: issue inactive since 450 days. Please update the issue or close it

[vemv]

Between https://github.com/clojure-emacs/orchard#design and https://github.com/clojure-emacs/orchard#api-documentation it looks like we're well served :)

cljdoc fix is kind of in its way cljdoc/cljdoc#487

[bbatsov]

I meant this ticket more in the sense of explaining what the various APIs are supposed to do with more prose. Something like an overview of namespaces and essential functions, but I guess good ns and function docstrings, plus working cljdoc would be a good enough solution.

Generally my concern is that few people will understand from the README how are they supposed to use Orchard.

[Cyrik]

I agree with @bbatsov. I was confused when I first found orchard through nrpel.
A basic overview of the namespaces plus a few usage examples would be helpful for anyone seeing this for the first time.

[vemv]

Alright let's see what we can do :) I agree with I guess good ns and function docstrings, plus working cljdoc would be a good enough solution., in the end Orchard is essentially a bag of defns so there's not that much to understand