Update CONTRIBUTING.md
Update CONTRIBUTING.md

Adds to list of supported package managers and lists dependent languages and/or package managers. 

It took us several iterations to track down which languages we were missing. `rake check_dependencies` checks for the package managers, but does not verify that the required languages are also installed.
bspeck/LicenseFinder,pivotal/LicenseFinder,pivotal/LicenseFinder,tinfoil/LicenseFinder,sschuberth/LicenseFinder,bdshroyer/LicenseFinder,sschuberth/LicenseFinder,bdshroyer/LicenseFinder,bspeck/LicenseFinder,bspeck/LicenseFinder,tinfoil/LicenseFinder,sschuberth/LicenseFinder,tinfoil/LicenseFinder,pivotal/LicenseFinder,pivotal/LicenseFinder,pivotal/LicenseFinder,sschuberth/LicenseFinder,sschuberth/LicenseFinder,bspeck/LicenseFinder,tinfoil/LicenseFinder,pivotal/LicenseFinder,pivotal/LicenseFinder,tinfoil/LicenseFinder,bspeck/LicenseFinder,bdshroyer/LicenseFinder,bdshroyer/LicenseFinder,bdshroyer/LicenseFinder