Ignore Folders in solution file

I have a folder in my game project folder structure which has temp/mercurial files in it. I want this folder to be excluded from the Visual Studio Solution.
Right now it displayes something like:

/Source
  /MyProject
    /design docs
    /Private
    /Public
    /.hg
    ...

I want the directories ‘design docs’ and ‘.hg’ to be ignored by the Solution file generator.

Is there any way to do this?
Thanks in advance!