Update action.yml for Marketplace release

Author: joshmgross

Diff for: action.yml

@@ -1,4 +1,4 @@
-name: 'Send Slack Message'
+name: 'Slack Messenger'
 description: 'Sends a slack message'
 author: 'joshmgross'
 inputs:
@@ -13,4 +13,7 @@ inputs:
     description: 'The Slack channel ID'
 runs:
   using: 'node12'
-  main: 'dist/index.js'
+  main: 'dist/index.js'
+branding:
+  icon: 'mail'
+  color: 'green'