Show `*Labels` modules in labels tutorial

[cuihtlauac]

Add references and examples to the following standard library modules in the Labelled and Optional Arguments tutorial

• ArrayLabels
• BytesLabels
• StringLabels
• UnixLabels
• MoreLabels
• StdLabels

[jahielkomu]

Hello @cuihtlauac and @SaySayo and @sabine.
I'm an outreachy applicant, relatively new to Ocaml, I have my local setup working. I have been going through the code base for some days to better understand. I'm looking to make a contribution.
I would like to have an attempt this and ask that you assign it to me.
Please if there is any more information you can provide about the issue kindly do.

Thanks