House keeping for reproducibility

[janhenrikbern]

Hello @maziarraissi,

1. I added a requirements.txt to help people get started with your PINNs repository.
   That way, they can run pip3 install -r requirements.txt to get their virtual environment started.

2. I added a .gitignore file specific to python to prevent pycache folders to find their way into the repository.
   Additionally, I removed the old pycache folder.

Hope this is helpful.

[janhenrikbern]

Whoever has write access, please merge feel free to merge this.

[praksharma]

This code supports the results in a paper. I don't think they'll accept this PR.