diff --git a/README.md b/README.md
index 7f437f7b..f00e8154 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,17 @@
 # open-dis-cpp
 A C++ implementation of the Distributed Interactive Simulation (DIS) protocol
+
+## Git submodule
+This repository includes a git submodule for the XML descripton files. These
+files contain a machine-readable description of the DIS messages that are 
+translated into a language implementation. Since the XML file is shared across
+multiple languages, I'm trying to prevent between-language drift of the description
+file.
+
+You should only need this if you're regenerated the source code, which is unlikely.
+but if you are, bring in the submodule with
+
+~~~~
+git submodule init
+git submodule update
+~~~~