API document to explain how to use web map core

We need to sort out and articulate the API document for clients who want to integrate our map.
The document should explain how to use the core, and API of the core, for example: who to jump to a position of the map.

---

Some hints:

- Please read our [readme](https://github.com/Greenstand/treetracker-web-map-core#treetracker-web-map-core) for more information/guide/tutorial.
- Here is [an engineering book](https://greenstand.gitbook.io/engineering/) in Greenstand.
- To know more about our organization, visit our [website](https://greenstand.org).
- If you want to join the slack community (some resources need the community member's permission), please leave your email address.

Start with the repository README and its integration guide, then identify the web map core API entry points used by clients. Document how to integrate the core and how to move the map to a requested position. Done means the API document covers the core usage and includes a clear example for jumping to a map position.

Written by the indexing model from the issue text.