Add a note that pickling is supported.

Doc/lib/libparser.tex

@@ -275,6 +275,8 @@ Some of the functions defined which accept an AST object as their
 first argument may change to object methods in the future.
 
 Ordered and equality comparisons are supported between AST objects.
+Pickling of AST objects (using the \module{pickle} module) is also
+supported.
 
 \begin{datadesc}{ASTType}
 The type of the objects returned by \function{expr()},

Doc/libparser.tex

@@ -275,6 +275,8 @@ Some of the functions defined which accept an AST object as their
 first argument may change to object methods in the future.
 
 Ordered and equality comparisons are supported between AST objects.
+Pickling of AST objects (using the \module{pickle} module) is also
+supported.
 
 \begin{datadesc}{ASTType}
 The type of the objects returned by \function{expr()},