docs: fixed broken links

[vinckr]

Fixed a few broken links, .md in the url was the problem.

Related issue

Proposed changes

Checklist

• I have read the contributing guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security. vulnerability, I
  confirm that I got green light (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further comments

[aeneasr]

If you make changes to the versioned docs (dir versioned_docs) make sure to also include those in the regular docs as well (docs/docs) :) A bit complicated right now, I know...

[vinckr]

Ok!