docs: add more detail to changeset

Author: alfrol

.changeset/fair-poems-pull.md

@@ -6,4 +6,8 @@
 'twilio-run': major
 ---
 
-Remove Node.js 18 from supported versions
+**WHAT**: Remove Node.js 18 from supported versions.
+
+**WHY**: Node.js 18 is EOL and will not receive bug fixes or security upgrades. Users should migrate to Node.js 20 or 22.
+
+**BREAKING CHANGE**: Projects using `create-twilio-function`, `@twilio-labs/plugin-asset`, `@twilio-labs/plugin-serverless`, `@twilio-labs/serverless-twilio-runtime` or `twilio-run` will have to migrate to Node.js 20 or 22.