Update creating-certificates-for-ttt.md

unzip did not work for this file on macosx.  You get the error, "   skipping: vmware/Direct-certGen-Ubuntu12-LTS-64-bit/Direct certGen - Ubuntu 64-bit.vmdk  need PK compat. v4.5 (can do v2.1)".

Included instructions on how to get 7za to unzip it.