Update cron-connector example deployment instructions

We now have our own fork of the connector. Also added a page
so that people can learn cron expressions quickly.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

Author: alexellis

docs/reference/cron.md

@@ -188,17 +188,17 @@ spec:
 
 ## Cron Connector
 
-The [cron event connector](https://github.com/zeerorg/cron-connector) is an OpenFaaS event-connector which can be used to trigger functions on a timed-basis. It works with all OpenFaaS providers.
+The [cron-connector](https://github.com/openfaas-incubator/cron-connector) is an OpenFaaS event-connector which can be used to trigger functions on a timed-basis. It makes use of the OpenFaaS REST API, so it is capable of working with all OpenFaaS providers.
 
 ### Kubernetes
 
 * Deploy the connector
 
 ```sh
-curl -s https://raw.githubusercontent.com/zeerorg/cron-connector/master/yaml/kubernetes/connector-dep.yml | kubectl create --namespace openfaas -f -
+arkade install cron-connector
 ```
 
-* Now annotate a function with a `topic` to give it a schedule
+* Now annotate a function with a `topic` of `cron-function` and a `schedule` using a valid CRON expression:
 
 ```yaml
 # (Abridged YAML)
@@ -235,6 +235,8 @@ You'll see the function invoked every 5 minutes as per the schedule.
 
 To stop the invocations, remove the two annotations or remove the cron-connector deployment.
 
+If you would like to explore how to write CRON expressions, then see [https://crontab.guru/](https://crontab.guru/)
+
 ## Docker Swarm
 
 Docker Swarm has no concepts of scheduled tasks or cron, but we have a suitable recommendation which you can use with your OpenFaaS cluster. If you deploy a Jenkins master service, then you can use that to manage your scheduled tasks. It will handle distributed locking, concurrency and queueing.