Add Evaluation mode examples

I would like to get even more explicit here as this is not the easiest concept. What does it mean to support tags to anyone?
Can we say that it's those resources that can't be found through search, or those that don't have their own blade, or do you have any better idea? Just more examples would help as well, I think.

Author: Tbohunek

articles/governance/policy/concepts/definition-structure.md

@@ -74,6 +74,9 @@ are:
 - `all`: evaluate resource groups and all resource types
 - `indexed`: only evaluate resource types that support tags and location
 
+For example, resource `Microsoft.Network/routeTables` supports tags and location and would be evaluated in both modes.
+However, resource `Microsoft.Network/routeTables/routes` cannot be tagged, and would not be evaluated in `Indexed` mode.
+
 We recommend that you set **mode** to `all` in most cases. All policy definitions created through
 the portal use the `all` mode. If you use PowerShell or Azure CLI, you can specify the **mode**
 parameter manually. If the policy definition doesn't include a **mode** value, it defaults to `all`