docs(install): harmonize trademark notice to match README

QA second-pass review of Phase 2 Batch 1 (commit 79c17fd) caught a
wording mismatch: README's Trademark Notice ends with the sentence
"All other product names, logos, and brands are property of their
respective owners" but INSTALLATION's notice cut off before that
sentence. The two should say the same thing — divergence here
becomes drift waiting to happen and a public-doc audit gotcha.

No semantic change; appending one sentence to the INSTALLATION
notice so both files carry the identical disclaimer.

QA-finding class: doc-disclaimer-mismatch.

Author: RelativisticJet

INSTALLATION.md

@@ -338,4 +338,6 @@ When upgrading from an older version:
 Splunk, Splunk Enterprise, and Splunk Enterprise Security are
 registered trademarks of Splunk LLC in the United States and other
 countries. This project is an independent community tool — it is not
-affiliated with, endorsed by, or sponsored by Splunk LLC.
+affiliated with, endorsed by, or sponsored by Splunk LLC. All other
+product names, logos, and brands are property of their respective
+owners.