Add a kubectl tip for working with keys with dots

Author: tengqm

content/en/docs/reference/kubectl/cheatsheet.md

@@ -166,6 +166,10 @@ kubectl get pv --sort-by=.spec.capacity.storage
 kubectl get pods --selector=app=cassandra -o \
   jsonpath='{.items[*].metadata.labels.version}'
 
+# Retrieve the value of a key with dots, e.g. 'ca.crt'
+kubectl get configmap myconfig \
+  -o jsonpath='{.data.ca\.crt}'
+
 # Get all worker nodes (use a selector to exclude results that have a label
 # named 'node-role.kubernetes.io/master')
 kubectl get node --selector='!node-role.kubernetes.io/master'