fix: add email as messaging option to readme

Co-authored-by: Sacha Brouté <[email protected]>

Author: scastlara

README.md

@@ -128,6 +128,7 @@ And if you wish to specify a different file, you can do so with `sheriff patrol
 ### Messaging services
 
 - [x] [Slack](http://slack.com)
+- [] [Email]
 
 ### Scanners