shell completion for kustomize commands

cmd/config/docs/commands/completion.md

@@ -0,0 +1,20 @@
+## install-completion
+
+Install shell completion.
+
+### Synopsis
+
+Install shell completion for kustomize commands and flags -- supports bash, fish and zsh.
+
+    kustomize install-completion
+
+Registers the completion command with known shells (e.g. .bashrc, .bash_profile, etc):
+
+    complete -C /Users/USER/go/bin/kustomize kustomize
+
+Because the completion command is embedded in kustomize directly, there is no need to update
+it separately from the kustomize binary.
+
+To uninstall shell completion run:
+
+    COMP_UNINSTALL=1 kustomize install-completion