Docs: Add example of using `StringCache`

[DeflateAwning]

It would be awesome if there was an example of how the StringCache works on the StringCache docs page

The comment talks about "context managers", which I assume are copied directly from the Python docs. As Ruby doesn't have context managers though, I assume this would need to be exchanged for a closure in the explanation.

[ankane]

Hi @DeflateAwning, added in the commit above.

[DeflateAwning]

Thanks for adding this!

I was mostly under the impression that I could stick a bunch of operations inside that do block.

However, I get this error:

web-1      | NoMethodError (undefined method `group_by' for #<Polars::StringCache:0x000075d912edfbf0>):

Any advice? Should I make a new issue with a reproducable example?

[ankane]

A reproducible example would be good.