I want to write a specialized plugin for WebStorm that can provide help for a custom framework, are there any tutorials on how to do that?
As @CrazyCoder says there is no specific official guide to write a Webstorm plugin. The reason is that all plugins are written in the same way, but you can decide for which IDE it will be available.
I found this post very helpful to start building a Webstorm plugin.
There is no WebStorm specific guide available, plug-ins are created exactly the same way as for IntelliJ IDEA.
You are welcome to ask more specific questions in the forum.