Clarify packages in tutorial. Closes SF bug #616211.

Doc/tut/tut.tex

@@ -2556,6 +2556,9 @@ Sound/                          Top-level package
               ...
 \end{verbatim}
 
+When importing the package, Python searchs through the directories
+on \code{sys.path} looking for the package subdirectory.
+
 The \file{__init__.py} files are required to make Python treat the
 directories as containing packages; this is done to prevent
 directories with a common name, such as \samp{string}, from