update doc

resource_retriever/manifest.xml

@@ -2,9 +2,11 @@
   <description brief="resource_retriever">
 
    This package retrieves data from url-format files such as http://,
-   ftp://, etc., and loads the data into memory.  The package:// url
-   is translated into a local file:// url. The resourse retriever uses
-   the libcurl library. 
+   ftp://, package:// file://, etc., and loads the data into memory.
+   The package:// url for ros packages is translated into a local
+   file:// url.  The resourse retriever was initially designed to load
+   mesh files into memory, but it can be used for any type of
+   data. The resource retriever is based on the the libcurl library.
 
   </description>
   <author>Josh Faust (jfaust@willowgarage.com)</author>