Ontology guide update

[mereolog]

Description

This updates Ontology Guide file the descriptions of the new hygiene tests.

Fixes: #1746

Checklist:

• [X] I'm familiar with the FIBO developer quide. My contribution meets all the requirements described there.
• [X] My contribution follows the principles of best practices for FIBO.
• [X] My changes have been reconciled with latest master and no merge conflicts remain.
• [X] This PR is related to exactly one issue. The issue is referenced by using a GitHub keyword such as "fixes", "closes", or "resolves".
• [X] Hygiene tests have been applied by a PR with "(WIP)" in title.
• [X] The issue has been tested locally using a reasoner (for ontology changes).