Add an explicit note about indentation and the used Yaml block quote

Signed-off-by: beorn7 <beorn@grafana.com>

Author: beorn7

content/docs/practices/rules.md

@@ -47,6 +47,11 @@ conflicts and give you more useful metrics and alerts.
 
 ## Examples
 
+_Note the indentation style with outdented operators on their own line between
+two vectors. To make this style possible in Yaml, [block quotes with an
+indentation indicator](https://yaml.org/spec/1.2/spec.html#style/block/scalar)
+(e.g. `|2`) are used._
+
 Aggregating up requests per second that has a `path` label:
 
 ```