Update documentation to indicate relative path installs are not supported
Created by: bbodenmiller
As per @randx comment at https://github.com/gitlabhq/gitlabhq/issues/3788#issuecomment-19044568.
Created by: bbodenmiller
As per @randx comment at https://github.com/gitlabhq/gitlabhq/issues/3788#issuecomment-19044568.