Use GitHub as the source of documentation

[zbynek]

Description

The Wiki is no longer available, use this repository as source of documentation instead.

Submitter checklist

• [n/a] Link to JIRA ticket in description, if appropriate.
• [n/a] Change is code complete and matches issue description.
• [n/a] Appropriate unit or acceptance tests or explanation to why this change has no tests.
• [n/a] Reviewer's manual test instructions provided in PR description. See Reviewer's first task below.

Reviewer checklist

• Run the changes and verified the change matches the issue description.
• Reviewed the code.
• Verified that the appropriate tests have been written or valid explanation given.
• If applicable, test installing this plugin on the Jenkins instance.