Add zsh completion script (finally)

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

completion/kubectx.zsh

@@ -0,0 +1,12 @@
+#compdef kubectx
+
+KUBECTX="${HOME}/.kube/kubectx"
+PREV=""
+if [ -f "$KUBECTX" ]; then
+    # show '-' only if there's a saved previous context
+    PREV=$(cat "${KUBECTX}")
+    _arguments "1: :((-\:Back\ to\ ${PREV} \
+        $(kubectl config get-contexts | awk '{print $2}' | tail -n +2)))"
+else
+    _arguments "1: :($(kubectl config get-contexts | awk '{print $2}' | tail -n +2))"
+fi