Add a link to the Request log format page from Logging Sample Config (#16778)

changelog.d/16778.doc

+Add a link to the "Request log format" explainer on the "Logging sample config" documentation page.

docs/usage/configuration/logging_sample_config.md

@@ -11,6 +11,9 @@ Note that a default logging configuration (shown below) is created automatically
 the homeserver config when following the [installation instructions](../../setup/installation.md).
 It should be named `<SERVERNAME>.log.config` by default.
 
+Hint: If you're looking for a guide on what each of the fields in the "Processed request" log lines mean,
+see [Request log format](../administration/request_log.md).
+
 ```yaml
 {{#include ../../sample_log_config.yaml}}
 ```