Use bash completion for zsh completion

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

README.md

@@ -16,7 +16,7 @@ about how `kubectl` can manage contexts better.
 
 ## Example
 
-```
+```sh
 $ kubectx minikube
 Switched to context "minikube".
 
@@ -31,11 +31,11 @@ Context "dublin" set.
 Aliased "gke_ahmetb_europe-west1-b_dublin" as "dublin".
 ```
 
-[**Set up `bash` completion →**](completion/README.md)
+[Set up `bash` and `zsh` completion →](completion/README.md)
 
 ### Help wanted
 
-[ ] homebrew formula/tap
+[ ] homebrew formula/tap that installs the script and completions
 
 -----
 

completion/README.md

@@ -5,11 +5,15 @@ even faster to switch between contexts easily.
 
 Copy the `kubectx.bash` file to your HOME directory:
 
-    cp kubectx.bash ~/.kubectx.bash
+```sh
+cp kubectx.bash ~/.kubectx.bash
+```
 
 And source it in your `~/.bashrc` file by adding the line:
 
-    [ -f ~/.kubectx.bash ] && source ~/.kubectx.bash
+```sh
+[ -f ~/.kubectx.bash ] && source ~/.kubectx.bash
+```
 
 Start a new shell, type `kubectx`, then hit <kbd>Tab</kbd> to see the existing
 contexts.
@@ -17,3 +21,25 @@ contexts.
 You can Add `TAB: menu-complete` to your `~/.inputrc` to cycle through the
 options with <kbd>Tab</kbd>.
 
+## Zsh setup
+
+`zsh` can leverage the `bash` completion scripts. Copy the `kubectx.bash` file
+to your HOME directory:
+
+```sh
+cp kubectx.bash ~/.kubectx.bash
+```
+
+And add the following to your `.zshrc`:
+
+```sh
+[ -f ~/.kubectx.bash ] && source ~/.kubectx.bash
+```
+
+Start a new shell, type `kubectx`, then hit <kbd>Tab</kbd> to see the existing
+contexts. If it does not work, modify the line above to:
+
+```sh
+[ -f ~/.kubectx.bash ] && autoload bashcompinit && bashcompinit && \
+      source ~/.kubectx.bash
+```