Resolve #3335983 "Schema rename"

Closes #3335983

config/schema/slack.schema.yml

@@ -3,22 +3,22 @@ slack.settings:
   mapping:
     slack_webhook_url:
       type: uri
-      label: 'Webhook URL'
+      label: 'The Webhook URL from an "Incoming WebHooks" integration.'
     slack_channel:
       type: string
-      label: 'Default channel'
+      label: 'The channel name with # symbol, for example #general (or @username for a private message or a private group name).'
     slack_username:
       type: string
-      label: 'Default username'
+      label: 'The name of the Slack bot'
     slack_icon_type:
       type: string
       label: 'Type of image'
     slack_icon_emoji:
       type: string
-      label: 'Emoji code'
+      label: 'The emoji for the Slack bot'
     slack_icon_url:
       type: uri
-      label: 'Image URL'
+      label: 'The icon for the Slack bot'
     slack_link_names:
       type: boolean
-      label: 'Link names'
+      label: 'Link names in the message options'