About link

[valentinRyckaert]

Summary of changes

• Add a feature in tess.yml to add a link to the TeSS documentation
• Add redirection from each about route to the specific documentation page (helpful for create links to the docs on other pages)

Motivation and context

Linked to this pull request

A lot of information is both in the TeSS docs and on the TeSS about page.
The goal is to merge the about page information with the TeSS documentation, and so directly redirect to it.

Checklist

• I have read and followed the CONTRIBUTING guide.
• I confirm that I have the authority necessary to make this contribution on behalf of its copyright owner and agree to license it to the TeSS codebase under the BSD license.