Add doc for email templates

docs/components/services/mailer.md

@@ -39,7 +39,7 @@ npm install -g mjml
 
 It uses its own file extention (`.mjml`) and syntax that abstracts the whole layer of complexity related to responsive email design. Once the template done and the content updated we can convert the mjml syntax to html using the following command:
 
-```
+```bash
 mjml my-file.mjml -o my-file.html
 ```