Fix broken link in README.md

[R1j1t]

Summary

Custodian documentation link was wrong. Original link was //custodian instead of /custodian.

Also, I am not sure if below is the desired behavior:

Let me know if this should be added to this PR?

[shyuep]

Thanks

[R1j1t]

Hi @shyuep, thanks for approving the PR!

I want to get involved and contribute to materials project. Would you recommend some issues which I can work on?

[janosh]

@R1j1t Thanks for offering to help! What code bases would you like to work on/are you most familiar with?

We are always looking to add more tests. Is that sth for you?

Else, we're also in the process of compressing pymatgen test files in materialsproject/pymatgen#3132 which requires fixing some tests that don't work with compressed files yet.

[R1j1t]

I am currently using pymatgen for grain boundary generation but use ASE for most of my calculations. I plan to shift to pymatgen by end of the year and also setup custodian for my job submission.

So, working on tests would be a good starting point. Let me take a stab at materialsproject/pymatgen#3132! Thanks @janosh for this!

[janosh]

Maybe materialsproject/pymatgen#3132 is a bad example for getting started considering it's hugely out of date with the master branch.

Honestly any type of testing is helpful and maybe some simple edge case testing would be great. I think parts of pymatgen could be better tested when structures/composition have oxidation states or when optional attributes like Site.label are None. Feel free to jump in anywhere if you can find new edge cases to test.

[R1j1t]

Thanks so much @janosh. If that is the case, let me go through the the defect analysis(https://github.com/materialsproject/pymatgen-analysis-defects) code base and add test cases!

[janosh]

I'm sure @jmmshn will be happy to take any test contributions.