Changed Note to admonition

Not sure if I needed to include 

markdown_extensions:
  - markdown.extensions.admonition

docs/hooks/hook_civicrm_alterReportVar.md

@@ -20,8 +20,10 @@ This hook is used to add or modify display columns and filters.
 
 -   null
 
-## Note
-
+markdown_extensions:
+  - markdown.extensions.admonition
+  
+!! Note
 It is often more performant to change the report query on $varType == 'sql' than
 to do database lookups on each row in the rows in the $var array on 
 $varType == 'rows'.