Document YTT usage

Author: ccheetham

README.md

@@ -1,3 +1,13 @@
 # Steeltoe NetCoreToolService
 
 [![Build Status](https://dev.azure.com/SteeltoeOSS/Steeltoe/_apis/build/status/Initializr/SteeltoeOSS.NetCoreToolService?branchName=main)](https://dev.azure.com/SteeltoeOSS/Steeltoe/_build/latest?definitionId=45&branchName=main)
+
+## Generate Kubernetes Manifest
+
+```
+# default manifest
+$ ytt -f kubernetes
+
+# sample custom manifest, see kubernetes/defaults.yaml for available parameters
+$ ytt -f kubernetes -v replica_count=5
+```