Docs: Clarifies how to add Key/Value pairs (#31303)

docs/sources/variables/variable-types/add-custom-variable.md

@@ -24,7 +24,7 @@ For example, if you have server names or region names that never change, then yo
 
 ## Enter Custom Options
 
-1. In the **Values separated by comma** list, enter the values for this variable in a comma-separated list. You can include numbers, strings, other variables or key/value pairs separated by a colon.
+1. In the **Values separated by comma** list, enter the values for this variable in a comma-separated list. You can include numbers, strings, other variables or key/value pairs separated by a space and a colon, i.e. `key1 : value1,key2 : value2`.
 1. (optional) Enter [Selection Options]({{< relref "../variable-selection-options.md" >}}).
 1. In **Preview of values**, Grafana displays a list of the current variable values. Review them to ensure they match what you expect.
 1. Click **Add** to add the variable to the dashboard.