Format check 1993/plummer/README.md + add alt code

Alt code is so that one can see with modern systems what is actually
happening. The time to sleep is configurable.

1993/plummer/plummer.alt.c

@@ -0,0 +1 @@
+char*_,*O;main(S,l)char**l;{*(O=*(l+++S-1)-1)=13,*l[1]=0;for(;;)for(printf(*l),_=O-1,usleep(Z);_>=*l&&++*_>(S+*O+S)*S;*_--=(S+*O)*S);}