Use GitHub as the source of documentation

[zbynek]

• [x] Make sure you are opening from a topic/feature/bugfix branch (right side) and not your master branch!
• [x] Ensure that the pull request title represents the desired changelog entry
• [x] Please describe what you did
• [x] Link to relevant issues in GitHub or Jira
• [n/a] Link to relevant pull requests, esp. upstream and downstream changes
• [n/a] Ensure you have provided tests - that demonstrates feature works or fixes the issue

Moved documentation from obsolete Jenkins Wiki to GitHub (see https://issues.jenkins.io/browse/WEBSITE-637). Replaced broken link with https://docs.qameta.io/allure/#_jenkins

[vbragin]

Thank you, will be fixed in next release