git clone needs --recursive as external-modules/spark is a submodule

I think the because external-modules/spark is a submodule, the git clone command needs a `--recursive`. When I cloned without `--recursive` and tried to run the sample data example (./examples/demo_tiny.sh) I got this error: `No such file: Config file does not exist: /home/oamsalem/Downloads/multifish/external-modules/spark/nextflow.config` It was fixed when I cloned with `--recursive`