correct the directory which rake notes look by default [ci skip]

guides/source/command_line.md

@@ -470,7 +470,7 @@ app/models/article.rb:
 
 NOTE. When using specific annotations and custom annotations, the annotation name (FIXME, BUG etc) is not displayed in the output lines.
 
-By default, `rake notes` will look in the `app`, `config`, `lib`, `bin` and `test` directories. If you would like to search other directories, you can provide them as a comma separated list in an environment variable `SOURCE_ANNOTATION_DIRECTORIES`.
+By default, `rake notes` will look in the `app`, `config`, `db`, `lib` and `test` directories. If you would like to search other directories, you can provide them as a comma separated list in an environment variable `SOURCE_ANNOTATION_DIRECTORIES`.
 
 ```bash
 $ export SOURCE_ANNOTATION_DIRECTORIES='spec,vendor'