added "Under construction" to package comment

R=rsc
DELTA=2  (2 added, 0 deleted, 0 changed)
OCL=34196
CL=34199

src/pkg/big/nat.go

@@ -6,6 +6,8 @@
 // These are the building blocks for the operations on signed integers
 // and rationals.
 
+//	NOTE: PACKAGE UNDER CONSTRUCTION (use bignum for the time being)
+//
 // This package implements multi-precision arithmetic (big numbers).
 // The following numeric types are supported:
 //