[tex-eplain] fix the URL in README

[Karl Berry]

    -WWW:    http://www.cs.rice.edu/~dorai/eplain
    +WWW:    http://www.ccs.neu.edu/~dorai/eplain

I'd actually like to suggest that http://tug.org/eplain be advertised.
That should always work (at least as long as I'm involved with TUG and
Eplain :).

Ok, Dorai?

(Thanks Stepan.)