Mention the website repository

[bernhardreiter]

As with the new website structure, everyone can contribute to the improvement of the website, but contributing to this repository: https://github.com/oasis-open/csaf-documentation/

This should be indicated somewhere on the website itself, to make this more public.

The github symbol the upper right is already used for the TC repository of the CSAF standard, so my first idea is to do something at the bottom.

@vkrasnovyd care to come up with an idea?

[vkrasnovyd]

@bernhardreiter Footer seems to be the right location for such a link. How about the minimalistic change:

• Link target: https://github.com/oasis-open/csaf-documentation/blob/main/CONTRIBUTING.md
• Link text: "Contribute"
• Styling: right after the attribution information (with some spacing between these elements), the word is blue like the links in the header, font weight - normal.

[bernhardreiter]

* Link text: "Contribute"

The link text should be more specific that it is about the webpage. And it is also about contributions, but feedback and issues also. So Linking CONTRIBUTIONS.md is suboptimal.