doc: document --include-path option in dandi validate command

Author: candleindark

docs/source/cmdline/validate.rst

@@ -29,6 +29,13 @@ Options
     in the eventual result. Note: The separator used to separate the patterns is a
     comma (`,`), so no pattern should contain a comma.
 
+.. option:: --include-path PATH
+
+    Filter issues in the validation results to only those associated with the
+    given path(s). A validation issue is associated with a path if its associated
+    path(s) are the same as or falls under the provided path. This option can be
+    specified multiple times to include multiple paths.
+
 .. option:: --min-severity [HINT|WARNING|ERROR]
 
     Only display issues with severities above this level (HINT by default)