Wrong links to old, archived repository for specs

[mahlzahn]

• In specification, the linked changelog does not show the last changes
  

  reuse-website/site/content/en/spec-3.3.md

  Lines 21 to 22 in c9f6901

  	For the revision history of this specification, please see [the change
  	log](https://git.fsfe.org/reuse/docs/src/branch/stable/CHANGELOG.md).

• In the contribution guide: link to archived repo. How to contribute to the specs? Where to suggest changes?
  

  reuse-website/README.md

  Lines 37 to 40 in c9f6901

  	We welcome your pull requests and issue reports. Please be aware that
  	this repository does not contain the specification, tutorial, and FAQ,
  	so please direct your inquiry to [reuse
  	docs](https://github.com/fsfe/reuse-docs).