diff --git a/doc b/doc
deleted file mode 100644
index 66dc905..0000000
--- a/doc
+++ /dev/null
@@ -1 +0,0 @@
-undefined
\ No newline at end of file
diff --git a/doc b/doc
new file mode 160000
index 0000000..6735e1a
--- /dev/null
+++ b/doc
@@ -0,0 +1 @@
+Subproject commit 6735e1aaf8107afbddc68dcee7c6b02ec7497621