Updated README with better explanation

Tools/ARM-Templates/Onboarding/README.md

@@ -1,5 +1,5 @@
 # Onboard Azure Sentinel solution
 
-This ARM template, installs the Azure Sentinel solution (SecurityInsights) on top of an existing workspace.
+This ARM template, onboards a given Log Analytics workspace to Azure Sentinel.
 
 [![Deploy to Azure](https://aka.ms/deploytoazurebutton)](https://portal.azure.com/#create/Microsoft.Template/uri/https%3A%2F%2Fraw.githubusercontent.com%2FAzure%2FAzure-Sentinel%2Fmaster%2FTools%2FARM-Templates%2FOnboarding%2FOnboardSentinel.json)