Add detailed documentation for plugin development and integration

[trentknox]

The README mentions support for 1000+ plugins and a marketplace, but there is no clear documentation on how to develop and integrate custom plugins. Adding a detailed guide on plugin development, including API references, example plugins, and integration steps, would greatly enhance the developer experience and encourage community contributions.

[leafliber]

Hi Trent, thanks for the great suggestion! We actually have a plugin development guide here: https://docs.astrbot.app/en/dev/star/plugin-new.html However, you are totally right that we are lacking some examples in guide. For now, you can also check out the plugin marketplace for reference: https://plugins.astrbot.app Sorry about that this marketplace is currently in Chinese only, but a revamped one is coming very soon (most likely).

[EterUltimate]

@trentknox https://github.com/xunxiing/AstrBot-Skill.git
This is an agent friendly,development skill, please reference it