README.md: fix broken directory rule links (#544)

README.md

diff --git a/README.md b/README.md
index fd2e275..a4567db 100644
--- a/README.md
+++ b/README.md
@@ -61,10 +61,10 @@
 * [analysis_test](docs/analysis_test_doc.md)
 * [build_test](docs/build_test_doc.md)
 * [common_settings](docs/common_settings_doc.md)
-* [directories](docs/copy_directory_doc.md)
+* directories
     * [directory](docs/directory_doc.md)
-    * [directory_glob](docs/directory_glob.md)
-    * [subdirectory](docs/subdirectory_doc.md)
+    * [directory_glob](docs/directory_glob_doc.md)
+    * [subdirectory](docs/directory_subdirectory_doc.md)
 * [copy_directory](docs/copy_directory_doc.md)
 * [copy_file](docs/copy_file_doc.md)
 * [diff_test](docs/diff_test_doc.md)