diff --git a/doc/source/configuration.rst b/doc/source/configuration.rst
index 1f5797c..384ceee 100644
--- a/doc/source/configuration.rst
+++ b/doc/source/configuration.rst
@@ -427,6 +427,9 @@
 
       LIBS_FROM_GIT=python-keystoneclient,oslo.config
 
+Setting the variable to ``ALL`` will activate the download for all
+libraries.
+
 Virtual Environments
 --------------------