diff --git a/README.org b/README.org
index 8cc86b4b5fa2825d1f92cb0faa63627fb9c211d7..1511adad53743bc246f1680d191dc3504cc7da38 100644
--- a/README.org
+++ b/README.org
@@ -1,7 +1,7 @@
 #+title: =gtfs_of_oud2=
 #+date: <2025-04-23 mer.>
 
-=gtfs_of_oud2= is a suite of tools, written in Perl, to assist the development of GTFS feeds from =.oud2= OuDiaSecond diagram files. Though not supported, =gtfs_of_oud2= may as well be used to process legacy OuDia files.
+=gtfs_of_oud2= is a suite of tools, written in Perl, to assist the development of GTFS feeds from =.oud2= OuDiaSecond diagram files. Though not supported, =gtfs_of_oud2= could as well be used to process legacy OuDia files.
 
 * Usage
 For the time being, the suite only has a single utility, =oud2_parser.pl=. Please note that this does not return anything yet and simply prints the result of the parse to the standard output.
@@ -10,15 +10,24 @@ Sample diagram files are provided in the ~tests/dia~ directory.
 
 ** =oud2_parser.pl=
 
-Parse a single diagram file.
+Parse a diagram file set.
 
 #+begin_src bash
   oud2_parser.pl
   oud2_parser.pl <filename>.oud2
 #+end_src
 
-For now, if no file is provided, a default diagram file is used instead.
+The files located in =../oud2= i.e. in a folder called =oud2= located in the directory above this =README= will be processed. Note that the following hierarchy must be respected:
 
+#+begin_src text
+  oud2
+  |-- train
+  |   |-- dia1.oud2
+  |   |-- dia2.oud2
+  |   |-- ...
+#+end_src
+
+For now, =oud2_parser= only outputs information about used diagram files to the standard output.
 
 * Licensing