Add a recipe for snakemake

[mbhall88]

I would like a singularity container that I can use to run snakemake

Please add the container recipe to recipes/ (remember to name it correctly) and ensure it builds on your fork's Singularity Hub. (make sure there is a %test)

Once it is building on your fork, please put in a pull request (PR) to this repository to close this issue.