Add upgrade section for the release note

Author: vblagoje

releasenotes/notes/upgrade-ntlk-1e94de2d6f5dd3b6.yaml

@@ -1,2 +1,5 @@
 fixes:
-  - Upgrades ntlk to 3.9.1 as prior versions are affect by https://nvd.nist.gov/vuln/detail/CVE-2024-39705. Due to these security vulnerabilities, it is not possible to use custom NLTK tokenizer models with the new version (for example in PreProcessor).
+  - Upgrades ntlk to 3.9.1 as prior versions are affect by https://nvd.nist.gov/vuln/detail/CVE-2024-39705.
+upgrade:
+  - |
+    Upgrades ntlk to 3.9.1 as prior versions are affect by https://nvd.nist.gov/vuln/detail/CVE-2024-39705. Due to these security vulnerabilities, it is not possible to use custom NLTK tokenizer models with the new version (for example in PreProcessor). Users can still use built-in nltk tokenizers by specifying the language parameter in the PreProcessor. See PreProcessor documentation for more details.