pigz: add singularity files

src/singularity_modules/pigz/2.4/build.sh

+#/bin/sh
+sudo singularity build --force bin/pigz:2.4.sif src/singularity_modules/pigz/2.4/pigz.def
+singularity sign bin/pigz:2.4.sif

src/singularity_modules/pigz/2.4/pigz.def

+Bootstrap: docker
+From: ubuntu:18.04
+
+%labels
+MAINTAINER Laurent Modolo
+
+%post
+PIGZ_VERSION=2.4
+PACKAGES=pigz=${PIGZ_VERSION}*
+
+apt-get update && \
+apt-get install -y --no-install-recommends ${PACKAGES} && \
+apt-get clean
+
+%environment
+export PIGZ_VERSION=2.4
+export PACKAGES=pigz=${PIGZ_VERSION}*
+
+%runscript
+exec /bin/bash "$@"