Specify absolute path to dotnet and Harbor.Tagd.dll in docker entrypoint

[nlowe]

If you change the working directory in the container it doesn't start unless you override the entrypoint:

$ docker run -it --rm -v "$(pwd):/rules" -w /rules hylandsoftware/tagd check --config-file tagd.yml --verbosity verbose
Did you mean to run dotnet SDK commands? Please install dotnet SDK from:
  http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409