Add link to return to Mantik webpage

Summary

As Mantik user, I want to read a well rendered documentation that is consistent with the Mantik style so I can be sure I am on the correct homepage.

Acceptance Criteria

• Link to Mantik added
• Header color, font style, fontsize are consistent with Mantik main page
• Later point also true for high dpi monitors

Technical Information

Additional Notes / Information

Suggested Implementation

• Add link to return to Mantik main page
• Check consistency between header color (type of blue), font style and fontsize scaling for high dpi monitors (title of gitlab repo seems too small) between Mantik and Docs