Add Github Action to Check on OSX

[dipterix]

• Added github action to check automatically https://github.com/dipterix/hdf5r/actions/runs/1120438472
• Added bash script to manually install HDF5 on osx/linux https://github.com/dipterix/hdf5r/blob/master/.github/install_hdf5.sh

To use this script, simply run in terminal:

# HDF5 version
export HDF5_VERSION="1.12.1"

# Installation path, default is /usr/local/hdf5
export HDF5_DIR=/usr/local/hdf5

# Run script
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/dipterix/hdf5r/master/.github/install_hdf5.sh)"