Using Documenter.jl instead of a long README

Hi everyone,
Whenever I want to use PyCall.jl, I find myself scrolling around the README looking for the information I need. Would a classic web page built with Documenter.jl be more appropriate and extendable? I'd be happy to propose a PR if that is something you might consider.

Start by reviewing the README and the repository's existing documentation setup, then investigate how a Documenter.jl site would fit PyCall.jl. The issue is done only when the documentation scope and proposed structure are clearly defined and an agreed documentation change is prepared.

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