Add comment about updating docs
diff --git a/Tools/compiler/ast.txt b/Tools/compiler/ast.txt
index a235b99..f2c0c99 100644
--- a/Tools/compiler/ast.txt
+++ b/Tools/compiler/ast.txt
@@ -6,6 +6,9 @@
# ! this child is a sequence that contains nodes in it
# & this child may be set to None
# = ... a default value for the node constructor (optional args)
+#
+# If you add node types here, please be sure to update the list of
+# Node types in Doc/lib/asttable.tex.
Module: doc*, node
Stmt: nodes!
Decorators: nodes!