add docs

[baggepinnen]

This PR adds the example from the readme with some additional explanations, as well as a page with exported interface. Tutorials will come in a second PR

[baggepinnen]

I don't have permissions to change settings for this repo, but I believe we need to enable github pages and set up the Documenter key etc. for the docs to publish correctly.

[topolarity]

Live (publically) at https://juliacomputing.github.io/AllocCheck.jl/