Create docs repo at Oniro4OpenHarmony with GitHub pages

Create the base repo to hold all documentation related to Oniro for OpenHarmony workflows, guides, policies and enhancements.

GitHub pages uses Jekyl as static website generator. Documentation files itself are using the GitHub markdown syntax.

• Create docs repo with otterdog
• Bring basic README.md file and wiki content over (https://gitlab.eclipse.org/eclipse/oniro-core/ohos-planning/-/wikis/Getting-started)