[Doc] Added more doc about context managers and import

[lyrixx]

No description provided.

[bitprophet]

I appreciate the input, but this feels too...basic? to me. I try to write our docs with a "knows at least beginner Python" knowledge level, to do otherwise opens a large can of worms, complicates things, etc :(

So, things like "you may have seen context managers but you might not know about contextlib.nested" falls above that line, for example, but "import a variable/function in order to use/refer to it" falls well below it IMHO.