docs(python): Various improvements to docstrings and user guide

[braaannigan]

Closes #10974

As per #10974 the API docs for low_memory could explain a bit more what they do but also direct anyone looking at this to streaming.

The docs for some lazyframe methods have been expanded on to give a bit more info about streaming and related useful methods.

[stinodego]

Thanks for the PR. Not 100% sure about the wording here and there - I'll take another look tomorrow and make some minor amendments.

[braaannigan]

@stinodego I'm going to add a few more config examples in if that's ok. Will update in the next couple of days

[braaannigan]

@stinodego This is ready for review again. In addition to the earlier docstrings:

• closes Better docs around cloud readers #11399 by updating info on cloud readers
• Adds user guide info to contributing.md
• Adds some missing API links
• General update of existing I/O pages

[stinodego]

Thanks for the all the work here!

I looked at the docstrings - I made some adjustments and I have some some comments, please have a look.

I will now look at the user guide changes.

In the future, please break up your work into smaller PRs. That helps me review things more quickly.

[braaannigan]

Thanks for the all the work here!

I looked at the docstrings - I made some adjustments and I have some some comments, please have a look.

I will now look at the user guide changes.

In the future, please break up your work into smaller PRs. That helps me review things more quickly.

Sure, this did get out of hand

[stinodego]

A few comments on the user guide part as well.

Definitely some good stuff here, much improved from how it was before!

[stinodego]

Hm, all the improvements that I had pushed seem to have been overwritten...

I'm going to re-open this PR myself in two parts (docstrings & user guide) and copy the stuff in here.