I have not found anything useful except for the documentation, where I can learn Panda3d and Render pipeline? I haven’t found Render pipeline’s documentation.
It looks like the project’s GitHub page has information.
Specifically, if you scroll down on that main GitHub page to which I just linked, you should see the project’s “readme” file. Aside from containing information itself, that “readme” also links to other sources of information, by the looks of it.
The RenderPipeline documentation is in the wiki on its GitHub page: