[#24] Add docs warning about security issues with remote URLs
[#24] Add docs warning about security issues with remote URLs

I think most of the users won't be affected by these issues. It's better to err
on the cautious side, though.

sirex/datapackage-py,datapackages/datapackage-py,okfn/datapackage-py,sirex/datapackage-py,okfn/datapackage-model-py,okfn/datapackage-py,datapackages/datapackage-py,okfn/datapackage-model-py