Add Docker image reference to CLI

Signed-off-by: Alex Ellis (VMware) <[email protected]>

Author: alexellis

docs/cli/install.md

@@ -38,6 +38,14 @@ $version = (Invoke-WebRequest "https://api.github.com/repos/openfaas/faas-cli/re
 
 If you're running the faas-cli with `sudo` we recommend using `sudo -E` to pass through any environmental variables you may have configured such as a `http_proxy`, `https_proxy` or `no_proxy` entry.
 
+## Docker image
+
+The `faas-cli` is also available as a Docker image making it convenient for use in CI jobs such as with a Jenkins pipeline or a task in cron.
+
+https://hub.docker.com/r/openfaas/faas-cli/tags/
+
+There is no "latest" tag, so find the version of the CLI you want to use from the tags page on the Docker Hub. These correspond to the release from GitHub.
+
 ## Build from source
 
 The [contributing guide](../contributing) has instructions for building from source and for configuring a Golang development environment.