Explanation of cargo features and cfg directives

[paddymul]

I'm not sure if this is out of scope.

For the following function:
https://docs.pola.rs/api/rust/dev/polars_core/series/struct.Series.html#method.serialize_to_bytes
The wording Available on crate feature serde only. appears. I have tried many combinations of cargo.toml features and I can't seem to get it to work.

I suspect the reason is that those docs are for 0.51.0 and the default cargo.toml points at 0.49.1.

Still a little bit of explanation of "When you see this in the docs, edit your cargo.toml this way. then use #cfg... like this" would be helpful.

Finally for those linked docs, I can't figure out how to view them at 0.49.1. For the tutorial, could you link to the specific version of the docs that the tutorial is based on?