Remove 2023 folders and placeholder folders; add README.md to all content folders

[felker]

The empty folders are just noise and clutter the repo. We cant necessarily guarantee that the content from the 2023 folders is still in a working state

Remove/archive:

• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/tools
• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/python_notebook_containers
• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/fs_sharing
• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/extraMachineLearningMaterials
• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/darshan-hands-on
• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/couplingSimulationML

Missing README.md:

• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/visualization_io
• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/programmingModels
• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/mpi
• https://github.com/argonne-lcf/ALCF_Hands_on_HPC_Workshop/tree/master/Scikit-learn