Add addin to website to allow for automatic documentation

[gep13]

i.e. get your addin listed here:

http://cakebuild.net/addins

Have a look at this PR:

cake-build/website#152

This assumes that you have added XML Documentation to your addin, as described here:

http://cakebuild.net/docs/contributing/documentation

Let me know if you have any questions. Thanks!

[gep13]

@wk-j just wanted to touch base to see if you had thought about doing this. Thanks!