Creates the ZD Target Docs. (#29)

Author: JeffNeff

docs/images/zendesk-target/create-bridge-1.png

@@ -10,3 +10,4 @@ The following is a list of Triggermesh event Destinations known as Targets. Some
 * [Oracle](./oracle.md): Forward events to the Oracle Cloud.
 * [Slack](./slack.md): Forward events to Slack as messages to deliver immediately, scheduled, or as an update to a pre-existing message.
 * [Splunk](./splunk.md): Forward arbitrary events to Splunk
+* [Zendesk](./zendesk.md): Perform actions in Zendesk upon reception of certain events.

docs/images/zendesk-target/create-bridge-2.png

@@ -0,0 +1,97 @@
+# Event Target for Zendesk
+
+This event target receives [CloudEvents][ce] and uses the Zendesk API to either create a new ticket or tag an existing one.
+
+## Prerequisites
+
+A Zendesk API token is required to utilize this Target. The steps to obtain a token are outlined in the [Zendesk API Docs](https://support.zendesk.com/hc/en-us/articles/226022787-Generating-a-new-API-token-)
+
+## Deploying an Instance of the Target
+
+Open the Bridge creation screen and add a Target of type `Zendesk`.
+
+![Adding a Zendesk Target](../images/zendesk-target/create-bridge-1.png)
+
+In the Target creation form, provide a name to the event Target, and add the following information:
+
+* **Default Ticket Subject**: An optional ticket subject fallback if one is not provided in an incoming event.
+* **Zendesk Subdomain**: Name of the Zendesk [Subdomain][zd-subdom], without the `zendesk.com` domain or `https://` scheme.
+* **Zendesk Email**: Email address associated with the Zendesk account.
+* **Zendesk API Token**: Reference to a [TriggerMesh secret][tm-secret] containing a [token][zd-token] to communicate with the Zendesk API, as described in the previous section.
+
+![Zendesk Target form](../images/zendesk-target/create-bridge-2.png)
+
+After clicking the `Save` button, the console will self-navigate to the Bridge editor. Proceed by adding the remaining components to the Bridge.
+
+![Bridge overview](../images/zendesk-target/create-bridge-3.png)
+
+After submitting the bridge, and allowing some configuration time, a green check mark on the main _Bridges_ page indicates that the bridge with a Zendesk event Target was successfully created.
+
+![Bridge status](../images/bridge-status-green.png)
+
+For more information about using Zendesk, please refer to the [Zendesk documentation][docs].
+
+## Event Types
+
+A Zendesk event Target accepts the following [CloudEvent][ce] types:
+
+### com.zendesk.ticket.create
+
+Events of this type intend to create a new Zendesk ticket.
+
+This type expects a [JSON][ce-jsonformat] payload with the following properties:
+| Name  |  Type |  Comment |
+|---|---|---|
+| **subject**| string  |  The value of the subject field for this ticket |
+|  **body** |  string | The value of the body field for this ticket  |
+
+An example response from the Zendesk Target after consuming an event of this type:
+
+```json
+{
+ "id":165,
+ "url":"https://triggermesh.zendesk.com/api/v2/tickets/165.json",
+ "subject":"Hello",
+ "raw_subject":"Hello",
+ "description":"World",
+ "status":"open",
+ "requester_id":412584624334,
+ "submitter_id":412584624334,
+ "assignee_id":412584624334,
+ "group_id":360010761434,
+ "due_at":"0001-01-01T00:00:00Z",
+ "via":
+   {
+     "channel":"api",
+     "source":{"from":{},"to":{},"rel":""}},
+     "satisfaction_rating":{"id":0,"score":"","comment":""},
+     "brand_id":360004879834,
+     "allow_attachments":true,
+     "is_public":true,
+     "created_at":"2020-08-05T20:00:11Z",
+     "updated_at":"2020-08-05T20:00:11Z",
+     "collaborators":{},
+     "comment":{"created_at":"0001-01-01T00:00:00Z"
+   }
+}
+```
+
+### com.zendesk.tag.create
+
+Events of this type intend to assign a [tag][zd-tag] to a pre-existing Zendesk ticket.
+
+This type expects a [JSON][ce-jsonformat] payload with the following properties:
+| Name  |  Type |  Comment |
+|---|---|---|
+| **id** | int64 | The value of the id field for the ticket to be updated |
+| **tag** | string | The value of the tag to assign to this ticket |
+
+[ce]: https://cloudevents.io/
+[ce-jsonformat]: https://github.com/cloudevents/spec/blob/v1.0/json-format.md
+[tm-secret]:https://docs.triggermesh.io/guides/secrets/
+
+[docs]: https://developer.zendesk.com/rest_api
+
+[zd-token]: https://support.zendesk.com/hc/en-us/articles/226022787-Generating-a-new-API-token-
+[zd-subdom]: https://support.zendesk.com/hc/en-us/articles/221682747-Where-can-I-find-my-Zendesk-subdomain-
+[zd-tag]:https://support.zendesk.com/hc/en-us/articles/203662096-About-tags