Some brief documentation on running only checks (#364).

docs/how-to/backup-your-databases.md

@@ -189,8 +189,9 @@ system.
 would like to backup databases only and not source directories, you can omit
 `source_directories` entirely.
 
-In older versions of borgmatic, instead specify an empty `source_directories`
+<span class="minilink minilink-addedin">Prior to version 1.7.1</span> In older
-value, as it is a mandatory option prior to version 1.7.1:
+versions of borgmatic, instead specify an empty `source_directories` value, as
+it is a mandatory option there:
 
 ```yaml
 location:

docs/how-to/deal-with-very-large-backups.md

@@ -137,6 +137,23 @@ If you want to temporarily ignore your configured frequencies, you can invoke
 `borgmatic check --force` to run checks unconditionally.
 
 
+### Running only checks
+
+<span class="minilink minilink-addedin">New in version 1.7.1</span> If you
+would like to only run consistency checks without creating backups (for
+instance with the `check` action on the command-line), you can omit
+the `source_directories` option entirely.
+
+<span class="minilink minilink-addedin">Prior to version 1.7.1</span> In older
+versions of borgmatic, instead specify an empty `source_directories` value, as
+it is a mandatory option there:
+
+```yaml
+location:
+    source_directories: []
+```
+
+
 ### Disabling checks
 
 If that's still too slow, you can disable consistency checks entirely,