Document usage of system() (issue #221)

docs/admin.rst

@@ -245,6 +245,9 @@ Before using any scripts, you need to list them in
 :setting:`PRE_COMMIT_SCRIPTS` configuration variable. Then you can enable them
 at :ref:`subproject` configuration as :guilabel:`Pre commit script`.
 
+The hook script is executed using system() call, so it is evaluated in a shell.
+It is passed single parameter consisting of file name of current translation.
+
 The script can also generate additional file to be included in the commit. This
 can be configured as :guilabel:`Extra commit file` at :ref:`subproject`
 configuration. You can use following format strings in the filename:

docs/config.rst

@@ -228,6 +228,10 @@ For example you can allow script which does some cleanup:
         '/usr/local/bin/cleanup-translation',
     )
 
+.. note:: 
+   
+    The hook is executed using system() call, so it is evaluated in a shell.
+
 .. seealso:: :ref:`processing`
 
 .. setting:: REGISTRATION_OPEN