Documents how to use the istioctl tab completion file. (#4023)

content/docs/setup/kubernetes/download/index.md

@@ -51,3 +51,63 @@ To use the Istio release Helm chart repository, add the Istio release repository
 {{< text bash >}}
 $ helm repo add istio.io https://storage.googleapis.com/istio-release/releases/{{< istio_full_version >}}/charts/
 {{< /text >}}
+
+## `istioctl` tab completion
+
+If you are using Bash or ZSH, `istioctl` includes a helpful script that enables tab completion for the currently available `istioctl` commands.
+
+### Installing the `istioctl` tab completion file
+
+If you are using Bash, the `istioctl` tab completion file is located in the `tools` directory. To use it, copy the `istioctl.bash` file to your home directory, then add the following line to source the `istioctl` tab completion file from your `.bashrc` file:
+
+{{< text bash >}}
+$ source ~/istioctl.bash
+{{< /text >}}
+
+For ZSH users, an additional `istioctl` tab completion file is also located in the `tools` directory. In a similar fashion, you can copy the `_istioctl` file to your home directory, then source the `istioctl` tab completion file as follows:
+
+{{< text zsh >}}
+$ source < _istioctl
+{{< /text >}}
+
+{{< tip >}}
+If you get an error like `complete:13: command not found: compdef`, then add the following to the beginning of your `~/.zshrc` file:
+
+{{< text bash >}}
+$ autoload -Uz compinit
+$ compinit
+{{< /text >}}
+
+{{< /tip >}}
+
+You may also add the `_istioctl` file to a directory listed in the `FPATH` variable. To achieve this, place the `_istioctl` file in an existing directory in the `FPATH`, or create a new directory and add it to the `FPATH` variable in your `~/.zshrc` file.
+
+### Prerequisites for macOS
+
+If you are using macOS with the Bash shell, make sure that the `bash-completion` package is installed. If you are using the [brew](https://brew.sh) package manager for macOS, you can check to see if the `bash-completion` package is installed with the following command:
+
+{{< text bash >}}
+$ brew info bash-completion
+bash-completion: stable 1.3 (bottled)
+{{< /text >}}
+
+If the bash-completion package is _not_ installed, proceed with installing the bash-completion package with the following command:
+
+{{< text bash >}}
+$ brew install bash-completion
+{{< /text >}}
+
+{{< tip >}}
+Once the bash-completion package has been installed on your macOS system, also make sure to add the following line to your `~/.bash_profile` file:
+
+`[[ -r "/usr/local/etc/profile.d/bash_completion.sh" ]] && . "/usr/local/etc/profile.d/bash_completion.sh"`
+{{< /tip >}}
+
+## Using `istioctl` auto-completion
+
+If the `istioctl` completion file has been installed correctly, press the Tab key while writing an `istioctl` command, and it should return a set of command suggestions for you to choose from:
+
+{{< text bash >}}
+$ istioctl proxy-<TAB>
+proxy-config proxy-status
+{{< /text >}}