Update docstring for walk

Signed-off-by: Jono Yang <jyang@nexb.com>

Author: JonoYang

src/commoncode/fileutils.py

@@ -375,6 +375,9 @@ def walk(location, ignored=None, allow_symlinks=False):
      - optionally ignore files and directories by invoking the `ignored`
        callable on files and directories returning True if it should be ignored.
      - location is a directory or a file: for a file, the file is returned.
+
+     If `allow_symlinks` is True, then symlinks will not be ignored and be
+     collected like regular files and directories
     """
     if on_linux and py2:
         location = fsencode(location)