Add warning about user formats
Add warning about this capability being experimental
@@ -12,6 +12,11 @@ User-defined formats allow users to write their own adaptors for the
netCDF C library, so that it can read and (optionally) write a
proprietary format through the netCDF API.
+This capability is currently experimental. It involves the exposing of internal
+netcdf interfaces and data structures that were previously invisible to users.
+This means that it is unstable and the exposed interfaces are subject to change.
+Use with caution.
+
User-defined format code is packaged into a separate library, the
user-defined format dispatch library. This library, when linked with
the netCDF library, will allow user programs to read their proprietary
