Updated docs. Fixed YAML newlines

Signed-off-by: Julien Duchesne <julien.duchesne@grafana.com>

config/testdata/conf.slack-both-file-and-url.yml

@@ -11,4 +11,3 @@ receivers:
   slack_configs:
   - channel: '#alerts1'
     text: 'test'
-

config/testdata/conf.slack-default-api-url-file.yml

@@ -19,4 +19,3 @@ receivers:
   - channel: '#alerts3'
     text: 'test'
     api_url: 'http://mysecret.example.com/'
-

config/testdata/conf.slack-no-api-url.yml

@@ -6,4 +6,4 @@ receivers:
 - name: 'slack-notifications'
   slack_configs:
   - channel: '#alerts'
-    text: 'test'
+    text: 'test'

docs/configuration.md

@@ -81,6 +81,7 @@ global:
 
   # The API URL to use for Slack notifications.
   [ slack_api_url: <secret> ]
+  [ slack_api_url_file: <filepath> ]
   [ victorops_api_key: <secret> ]
   [ victorops_api_url: <string> | default = "https://alert.victorops.com/integrations/generic/20131114/alert/" ]
   [ pagerduty_url: <string> | default = "https://events.pagerduty.com/v2/enqueue" ]
@@ -567,8 +568,10 @@ an [attachment](https://api.slack.com/docs/message-attachments).
 # Whether or not to notify about resolved alerts.
 [ send_resolved: <boolean> | default = false ]
 
-# The Slack webhook URL.
+# The Slack webhook URL. Either api_url or api_url_file should be set.
+# Defaults to global settings if none are set here.
 [ api_url: <secret> | default = global.slack_api_url ]
+[ api_url_file: <filepath> | default = global.slack_api_url_file ]
 
 # The channel or user to send notifications to.
 channel: <tmpl_string>

docs/notification_examples.md

@@ -13,6 +13,8 @@ In this example we've customised our Slack notification to send a URL to our org
 
 ```
 global:
+  # Also possible to place this URL in a file.
+  # Ex: `slack_api_url_file: '/etc/alertmanager/slack_url'`
   slack_api_url: '<slack_webhook_url>'
 
 route: