Documentation: OpenSCD-core API

[Sander3003]

As developer I would like to how how the openSCD-core API works So I can develop a plug-in for it.

What needs to be done: Markdown with a description how the openSCD-core works

Acceptance criteria:

• [ ] Document the events supported in openscd core
• [ ] Example code how to interact with the open/close docs and the editing api in OpenSCD-core
• [ ] Update the readme.md
• [ ] Location: https://github.com/openscd/open-scd/blob/main/packages/core/README.md

Inspiration: https://storybook.js.org/docs/get-started/install