Add sample block

Author: MythreyaK

config.md

@@ -371,10 +371,19 @@ Possible values: `None` (default), `Strict`.
 
 ## Completion
 
+Configures code completion features. Sample block (default):
+
+```yaml
+Completion:
+    AllScopes: Yes
+    ArgumentLists: FullPlaceholders
+    HeaderInsertion: Never
+```
+
 ### AllScopes
 {:.v13}
 Whether code completion should include suggestions from scopes that are
-not visible. The required scope prefix will be inserted.
+not visible. The required scope prefix will be inserted. Default is `Yes`.
 
 ### ArgumentLists
 {:.v20}