Update javascript-angular-plugin.md

Add note informing customers about Angular version updates

Author: mattmccleary

articles/azure-monitor/app/javascript-angular-plugin.md

@@ -21,6 +21,9 @@ The Angular plugin for the Application Insights JavaScript SDK, enables:
 > [!WARNING]
 > Angular plugin is NOT ECMAScript 3 (ES3) compatible.
 
+> [!IMPORTANT]
+> When we add support for a new Angular version, our NPM package becomes incompatible with down-level Angular versions. Continue to use older NPM packages until you're ready to upgrade your Angular version.
+
 ## Getting started
 
 Install npm package: