Adding initial doc for func subscribe (#5754)

* Adding initial doc for func subscribe

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* correction

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* Adding hint for deploy

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* Adding index

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

* Updates

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

---------

Signed-off-by: Matthias Wessendorf <mwessend@redhat.com>

config/nav.yml

@@ -88,6 +88,7 @@ nav:
       - Creating functions: functions/creating-functions.md
       - Building functions: functions/building-functions.md
       - Running functions: functions/running-functions.md
+      - Subscribing functions: functions/subscribing-functions.md
       - Deploying functions: functions/deploying-functions.md
       - Invoking functions: functions/invoking-functions.md
       - Language packs: functions/language-packs.md

docs/functions/subscribing-functions.md

@@ -0,0 +1,37 @@
+# Subscribe functions to CloudEvents
+
+### Prerequisites
+
+- Knative Eventing installed on the cluster
+
+### Procedure
+
+--8<-- "proc-subscribe-function.md"
+
+### Deployment with Triggers
+
+When invoking `func deploy` the CLI will create Knative Triggers for the function.
+
+=== "func"
+
+    Deploy the function with Triggers by running the command inside the project directory:
+
+    ```bash
+    func deploy
+    ```
+
+=== "kn func"
+
+    Deploy the function with Triggers by running the command inside the project directory:
+
+    ```bash
+    kn func deploy
+    ```
+
+!!! Success "Expected output"
+    ```{ .bash .no-copy }
+        🙌 Function image built: <registry>/hello:latest
+        🎯 Creating Triggers on the cluster
+        ✅ Function deployed in namespace "default" and exposed at URL:
+        http://hello.default.127.0.0.1.sslip.io
+    ```

docs/snippets/proc-subscribe-function.md

@@ -0,0 +1,33 @@
+<!-- Snippet used in the following topics:
+- /docs/functions/subscribing-functions.md
+-->
+The `subscribe` command will connect the function to a set of events, matching a series of filters for Cloud Event metadata
+and a Knative Broker as the source of events, from where they are consumed.
+
+=== "func"
+
+    To subscribe the function to events for a given broker, run the following command:
+
+    ```bash
+    func subscribe --filter type=com.example --filter extension=my-extension-value --source my-broker
+    ```
+
+    To subscribe the function to events for the default broker, run the following command:
+
+    ```bash
+    func subscribe --filter type=com.example --filter extension=my-extension-value
+    ```
+
+=== "kn func"
+
+    To subscribe the function to events for a given broker, run the following command:
+
+    ```bash
+    kn func subscribe --filter type=com.example --filter extension=my-extension-value --source my-broker
+    ```
+
+    To subscribe the function to events for the default broker, run the following command:
+
+    ```bash
+    kn func subscribe --filter type=com.example --filter extension=my-extension-value
+    ```