should document reading from .vcf.gz over .vcf

Got bitten by this.  Refiltered our vcf and gave it the same filename as previously.  Tried to reload into Gemini but changes not reflected in Gemini database.  Eventually figured out that Gemini was silently loading from the already-existing .gz file (from before the refiltering of the vcf).

My suggestion is that either this behavior (reading from .vcf.gz if exists) should either be documented or Gemini should provide some feedback like "my.vcf.gz already exists.  Reading from my.vcf.gz"