Readme fixes.

Author: dmitry-ivanov

README.md

@@ -28,7 +28,6 @@ Logging and notifications for Laravel console commands.
   - [File channel](#file-channel)
   - [Notification channels](#notification-channels)
     - [Email channel](#email-channel)
-    - [Slack channel](#slack-channel)
     - [Database channel](#database-channel)
 - [Error handling](#error-handling)
   - [Custom exceptions](#custom-exceptions)
@@ -189,12 +188,6 @@ class ExampleCommand extends Command
 }
 ```
 
-### Slack channel
-
-Slack channel provides notifications via Slack.
-
-This channel is not implemented yet. If you need it, let [me](mailto:[email protected]) know and I'll try to make it faster.
-
 ### Database channel
 
 Database channel provides saving of notifications into the database.