SOLR-15398: Faceting page in ref guide doesn't mention the json.nl parameter

[epugh]

Description

json.nl is important when faceting.

Solution

link in ref guide.

Tests

Please describe the tests you've developed or run to confirm this patch implements the feature or solves the problem.

Checklist

Please review the following and check all that apply:

• [ x] I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• [ x] I have created a Jira issue and added the issue ID to my pull request title.
• [ x] I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• [ x] I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• [x ] I have added documentation for the Reference Guide

[epugh]

Thanks! Going to merge.