diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..afc4a0a
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "book"]
+	path = book
+	url = ./
diff --git a/book b/book
new file mode 160000
index 0000000..75df8b8
--- /dev/null
+++ b/book
@@ -0,0 +1 @@
+Subproject commit 75df8b8750b87414513bfb6e7bbec041b3b80e88