Add README.md to docs dir.

[DavidSagan]

No description provided.

[mattsignorelli]

This should probably be in a For Developer's section of the documentation. Do you agree?

For the index.md part of the documentation, we can automatically include the github README by adding this into the make.jl file:

cp(joinpath(@__DIR__, "..", "README.md"), joinpath(@__DIR__, "src", "index.md"); force=true)

[DavidSagan]

I was imagining that only developers would look at the docs area so no need of a developers section. But if you want it, it is fine with me. Just tell me what you think.

[DavidSagan]

Also at this point in time my inclination is to not automatically copy the github README.md file to the docs since the file has extra stuff to display build status.

[DavidSagan]

By the way, I tried to put the cp command in make.jl and it caused the server to go in an infinite loop.