Add a requirements.txt file

[spykelionel]

Most contributors face issues trying to run the project or generating a heatmap_betweenness_centrality_timing.png as a stated in #191

[Schefflera-Arboricola]

hi @spykelionel there will be a different infrastructure for benchmarking, it's a WIP (issue #12). Also, in networkx the requirements files are auto-generated from the pyproject.toml file and not manually. So, you should consider making changes there, if any!
for the outreachy task pip install networkx matplotlib seaborn nx_parallel pandas is enough ig.

Thank you :)

[spykelionel]

Thanks for the update @Schefflera-Arboricola. I have updated the requirements.txt to match the description above

[Schefflera-Arboricola]

@spykelionel No, I meant we probably won't be generating heatmaps for benchmarking in the future. And that pip command would be enough to complete the outreachy task.

Also, in networkx the requirements files are auto-generated from the pyproject.toml file and not manually.

Thank you :)