docs: extend the General naming rule to main use cases

The naming rule only covered catch-all subcategories, but CLI Development > CLI Development and HTTP Clients > Clients were main use cases that repeated their section's name and were renamed General too, so the rule did not describe the practice.

Co-Authored-By: Claude <noreply@anthropic.com>

CONTRIBUTING.md

@@ -98,7 +98,7 @@ Adding sections or subcategories is maintainer-only (see Admission). For maintai
 3. Add the section title to the Table of Contents under its group
 4. Order entries per Entry Ordering above
 
-Name a section's catch-all subcategory General, never the section's own name: a subcategory named like its section competes with the section page in search results.
+A subcategory never repeats its section's name: one named like its section competes with the section page in search results. Name the section's catch-all or main use case General instead.
 
 ## Review Process