Update vpn.md (#93)

Before Submitting This PR, Please Ensure You Have Completed The
Following:

1. [x] Are internal links to wiki documents using [relative file
links](https://docusaurus.io/docs/markdown-features/links)?
2. [x] Are all new documentation files lowercase, with dash separated
names (ex. unraid-os.mdx)?
3. [x] Are all assets (images, etc), located in an assets/ subfolder
next to the .md/mdx files?
4. [x] Have you checked to ensure there aren't other open [Pull
Requests](../../../pulls) for the same update/change?
5. [x] Is the build succeeding?