Chore: Add guide for how to use eventHook to send updates to Slack (#459)

* Add guide for how to use eventHook to send updates to Slack

* better slack url

* use require instead of import

docs/getting-started.md

@@ -59,7 +59,7 @@ Available unleash options include:
   - `custom` - use this when you implement your own custom authentication logic.
 - **ui** (object) - Set of UI specific overrides. You may set the following keys: `headerBackground`, `environment`, `slogan`.
 - **getLogger** (function) - Used to register a [custom log provider](#How do I configure the log output).
-- **eventHook** (`function(event, data)`) - If provided, this function will be invoked whenever a feature is mutated. The possible values for `event` are `'feature-created'`, `'feature-updated'`, `'feature-archived'`, `'feature-revived'`. The `data` argument contains information about the mutation. Its fields are `type` (string) - the event type (same as `event`); `createdBy` (string) - the user who performed the mutation; `data` - the contents of the change. The contents in `data` differs based on the event type; For `'feature-archived'` and `'feature-revived'`, the only field will be `name` - the name of the feature. For `'feature-created'` and `'feature-updated'` the data follows a schema defined in the code [here](https://github.com/Unleash/unleash/blob/master/lib/routes/admin-api/feature-schema.js#L38-L59).
+- **eventHook** (`function(event, data)`) - If provided, this function will be invoked whenever a feature is mutated. The possible values for `event` are `'feature-created'`, `'feature-updated'`, `'feature-archived'`, `'feature-revived'`. The `data` argument contains information about the mutation. Its fields are `type` (string) - the event type (same as `event`); `createdBy` (string) - the user who performed the mutation; `data` - the contents of the change. The contents in `data` differs based on the event type; For `'feature-archived'` and `'feature-revived'`, the only field will be `name` - the name of the feature. For `'feature-created'` and `'feature-updated'` the data follows a schema defined in the code [here](https://github.com/Unleash/unleash/blob/master/lib/routes/admin-api/feature-schema.js#L38-L59). See an example [here](./guides/feautre-updates-to-slack.md).
 
 ### 3. Docker
 

docs/guides/feautre-updates-to-slack.md

@@ -0,0 +1,76 @@
+# Add Slack hook to Unleash
+
+## Create a custom Slack WebHook url:
+
+1. Go to [https://slack.com/apps/manage/custom-integrations](https://slack.com/apps/manage/custom-integrations)
+1. Click Incoming WebHooks
+1. Click “Add Configuration”
+1. This is Slack's help page on how to do this: https://api.slack.com/custom-integrations/incoming-webhooks
+   - Choose a channel, follow the wizard, get the custom URL.
+
+## Send data to Slack using an event hook function
+
+Using the `eventHook` option, create a function that will send the data you'd like into Slack when mutation events happen.
+
+```javascript
+const unleash = require('unleash-server');
+const axios = require('axios');
+
+function onEventHook(event, eventData) {
+  const { createdBy: user, data } = eventData;
+  let text = '';
+
+  const unleashUrl = 'http://your.unleash.host.com';
+  const feature = `<${unleashUrl}/#/features/strategies/${data.name}|${
+    data.name
+  }>`;
+
+  switch (event) {
+    case 'feature-created':
+    case 'feature-updated': {
+      const verb =
+        event === 'feature-created' ? 'created a new' : 'updated the';
+      text = `${user} ${verb} feature ${feature}\ndescription: ${
+        data.description
+      }\nenabled: ${data.enabled}\nstrategies: \`${JSON.stringify(
+        data.strategies,
+      )}\``;
+      break;
+    }
+    case 'feature-archived':
+    case 'feature-revived': {
+      const verb = event === 'feature-archived' ? 'archived' : 'revived';
+      text = `${user} ${verb} the feature ${feature}`;
+      break;
+    }
+    default: {
+      console.error(`Unknown event ${event}`);
+      return;
+    }
+  }
+
+  axios
+    .post(
+      'https://hooks.slack.com/services/THIS_IS_WHERE_THE_CUSTOM_URL_GOES',
+      {
+        username: 'Unleash',
+        icon_emoji: ':unleash:', // if you added a custom emoji, otherwise you can remove this field.
+        text: text,
+      },
+    )
+    .then(res => {
+      console.log(`Slack post statusCode: ${res.status}. Text: ${text}`);
+    })
+    .catch(error => {
+      console.error(error);
+    });
+}
+
+const options = {
+  eventHook: onEventHook,
+};
+
+unleash.start(options).then(server => {
+  console.log(`Unleash started on http://localhost:${server.app.get('port')}`);
+});
+```