Warn against GND for IsName

[nomeata]

I just had a hard time debugging a problem here; the reason was that

newtype WordN = WordN Int deriving (Show, Ord, Eq, Typeable, IsName)

did not make WordN 1 and 1 :: Int different names. The proper code would be

newtype WordN = WordN Int deriving (Show, Ord, Eq, Typeable)
instance IsName

I think the documentation of IsName should comment on that, and maybe give the latter as the suggested way to have dedicated names.

[byorgey]

Thanks!