Document the discussion in #33

[ceridwen]

When I went to try to figure out what the purpose of the adapter argument to wrapt.decorator, which I only found by reading the code, I eventually ended up reading through the closed issue because it wasn't otherwise documented. A brief summary, possibly with some of the examples used in the issue, would be useful somewhere in the docs, maybe under an "Advanced Usage" or similar heading?

[GrahamDumpleton]

Although the whole discussion wasn't transplanted to the docs, it does seem that details of the adapter factory were added, so going to close out this issue now. For more in depth discussion of background the other GitHub issue exists.