fix doc links

[jcrben]

These links are broken, so this fixes them.

Reproduction:

• go to https://github.com/hashicorp/packer-plugin-virtualbox/tree/main/docs
• click the virtualbox-iso link
• see this:
• 

Verify fix:

• go to my fork's branch: https://github.com/jcrben/packer-plugin-virtualbox/tree/fix-doc-links/docs
• click the same link
• it works: https://github.com/jcrben/packer-plugin-virtualbox/tree/fix-doc-links/docs

[hashicorp-cla]

All committers have signed the CLA.

[nywilken]

Hi @jcrben thanks for change. The links in the README are configured for the integration portal on https://developer.hashicorp.com/packer/integrations/hashicorp/virtualbox

I understand how this can be confusing when trying to read the documents on GitHub. Plugin documents contain a number of generation steps and partials, which then get pushed into .web-docs for final deployment on the integration portal.

I closed this PR, as this is the expected behavior. But feel free to open an issue if you wish to discuss this further. I do wonder if there is a flow we can introduce for converting the links upon generation 🤔