docs: fix formatting for behaviour docs (#1022)

The missing newline meant this wasn't parsed as a bullet list

Author: mistydemeo

docs/docs/user-guide/behaviors.md

@@ -89,6 +89,7 @@ docker run -v $PWD/test-crawls:/crawls webrecorder/browsertrix-crawler crawl --u
 ## Creating Custom Behaviors
 
 A custom behavior file can be in one of the following supported formats:
+
 - JSON User Flow
 - JavaScript / Typescript (compiled to JavaScript)