Update wiki information

[beppler]

Pull request #19 updated the type mappings for SQL Server.

I updated the documentation for this on wiki on my fork, but Github does not have a way to send a pull request for wiki.

Then the following commands can be used to pull the changes on wiki on my fork to wiki of this project:

git clone https://github.com/SharpTools/sharpdata.wiki.git sharpdata-wiki
cd sharpdata-wiki
git remote add beppler https://github.com/beppler/sharpdata.wiki.git
git fetch beppler
git merge beppler/master
git remote remove beppler
git push

This will merge the change and update wiki pages on project to match the current implementation.