Update README.txt to reflect new admin menu structure for configuration pages

Problem/Motivation

The current README.txt shows direct links to the settings pages, but it doesn’t reflect the updated menu structure. Now, both settings pages are grouped under Configuration → AI → AI Webform Guard.

Steps to reproduce

Proposed resolution

Update the Configuration section of the README.txt to reflect this improved structure.
You can now access all configuration options for AI Webform Guard under:
Administration → Configuration → AI → AI Webform Guard

Remaining tasks

User interface changes

API changes

Data model changes