Initial gitignore file for [Cadence Virtuoso](http://www.cadence.com/products/cic/Pages/default.aspx)

Cadence Virtuoso is a commercial EDA tool used for custom IC (ASIC) design. This gitignore file
blacklists database lock files, the contents of run directories for layout versus schematic and
design rule checks as well as log files for a selection of tools inside the package.