docs: improve docs

Author: eddyerburgh

docs/en/api/config.md

@@ -85,12 +85,12 @@ VueTestUtils.config.provide['$logger'] = {
 - type: `Boolean`
 - default: `true`
 
-Logs warning when extended child components are automatically stubbed. Hides warnings when set to `false`.
+Logs warning when extended child components are automatically stubbed. Hides warnings when set to `false`. Unlike other config options, this cannot be set on the mounting options.
 
 Example:
 
 ```js
 import VueTestUtils from '@vue/test-utils'
 
 VueTestUtils.config.logModifiedComponents = false
-```
+```