Add a note to the module page and README.md for rendered entity as select options

Problem/Motivation

I tried this module as I was looking for a way to show rendered entities in a certain view mode as entity reference radio / checkbox options.
This module has a different purpose, but I didn't find the solution, so maybe others may also run into this.

If you like the idea to describe the solution for the different goal, you can find it here: ✨ Allow to use rendered entities (in selected view mode) as webform entity checkboxes / radios options Active

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes