Update README.md.

README.md

-**Please** **do** **not** use the download button on the top right; use this
-link instead:
-[http://smt-lib.loria.fr/zip/QF_DT.zip](http://smt-lib.loria.fr/zip/QF_DT.zip)
-
 This is a repository of SMT-LIB benchmarks.
 See [http://smtlib.org](http://smtlib.org) for more information about the
 SMT-LIB initiative.