Documentation improvements collection

In this issue, I want to collect topics and improvements for the documentation.

- Simplified getting started with platform specific hints
- Simplified ["Singleton service"](https://github.com/capacitor-community/sqlite/blob/master/docs/Ionic-Angular-Usage.md) with better readability
- Platform specific quirks and hints
- e.g. on `web` we have to call `saveToStore` programmatically. `closeConnection` also does `saveToStore`
- What is the difference between `run`, `query`, `execute` and `executeSet`?
- Detailed information on connection management
- Detailed information on how db versioning works

**FAQ:**

- How to drop a database? (advice: close connection afterwards)

Maybe we could implement some documentation website with a framework like https://github.com/facebook/docusaurus