reword the comment explaining readDirectory()

Change-Id: I2f3504946b28721b2e98eb060becc9a9fc49ca0f
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>

src/fileutils.h

@@ -74,8 +74,8 @@ namespace ring { namespace fileutils {
 
     /**
      * Read content of the directory.
-     * The result is a list of full paths of files in the directory,
-     * without "." and "..".
+     * The result is a list of relative (to @param dir) paths of all entries
+     * in the directory, without "." and "..".
      */
     std::vector<std::string> readDirectory(const std::string &dir);