add some documentation for symtable
diff --git a/Doc/library/language.rst b/Doc/library/language.rst
index bcf9ac0..3cc4b82 100644
--- a/Doc/library/language.rst
+++ b/Doc/library/language.rst
@@ -16,6 +16,7 @@
 
    parser.rst
    ast.rst
+   symtable.rst
    symbol.rst
    token.rst
    keyword.rst