Clarifying documentation for Cones

[MicahGale]

Description

This provides some clarification on how Cone surfaces are formed, to address some user confusion that occured.

Fixes #2891.

Checklist

• [ ] I have performed a self-review of my own code
• [ ] ~I have run clang-format (version 15) on any C++ source files (if applicable)~
• [ ] I have followed the style guidelines for Python source files (if applicable)
• [x] I have made corresponding changes to the documentation (if applicable)
• [ ] ~I have added tests that prove my fix is effective or that my feature works (if applicable)~