Added INFO alert type

Related to: https://gitlab.com/gitlab-org/gitlab-docs/-/merge_requests/2019

doc/development/documentation/styleguide/index.md

@@ -1374,6 +1374,7 @@ Alert boxes are generated when one of these words is followed by a line break:
 - `FLAG:`
 - `NOTE:`
 - `WARNING:`
+- `INFO:` (Marketing only)
 
 For example:
 
@@ -1430,6 +1431,21 @@ It renders on the GitLab documentation site as:
 WARNING:
 This is something to be warned about.
 
+### Info
+
+The Marketing team uses the `INFO` alert to add information relating
+to sales and marketing efforts.
+
+```markdown
+INFO:
+This info is important.
+```
+
+It renders on the GitLab documentation site as:
+
+INFO:
+This info is important.
+
 ## Blockquotes
 
 For highlighting a text inside a blockquote, use this format: