fix(content): fix some content issues

[Tirokk]

🍰 Pullrequest

Issues

• fixes #152

Todo

• [x] English: Contribute page: Delete the link "Organisierst du gerne?"
• [x] English: Contribute page: Change heading "Make the ocelot.social software known" to "Promote the ocelot.social software".
• [x] All languages: Contribute page: Operate your own network: Link to the "Get started" page (instead of the documentation).
• [ ] optimize screen shots, e.g. mouse pointer hand on hover
  • [ ] is an uninvestigated problem on @sushidave Firefox
• [x] optimize button design with dark mode: use a darker green, e.g. #077107