Add missing layer in map example for @turf/line-split docs

[luc-tielen]

• Is this a bug fix, new functionality, or a breaking change?
• Have read and followed the steps for preparing a pull request.

Very simple PR, I noticed in the docs a layer was missing for line-split.
(You can't see the actual "split" result, see https://turfjs.org/docs/api/lineSplit#examples.)

[smallsaucepan]

Thanks for fixing this @luc-tielen. Could I please make a small request? To go above and beyond would you mind making the split line multi coloured? That will make the result easier to visualise.

If you expand the addToMap part to include the extra lines below, that should produce a map like the one shown.

 * //addToMap
 * var addToMap = [line, splitter, split]
 *
 * split.features[0].properties.stroke = "red";
 * split.features[1].properties.stroke = "blue";

Let us know when that is done we can merge this in!

[smallsaucepan]

Please also run pnpm run docs to regenerate the README.md and commit those changes too.

[luc-tielen]

Thanks @smallsaucepan for the suggestion, I didn't know this was possible.
I'm only "passing by" and noticed this in the docs using this (great!) library at work, so I didn't realize it was more than a simple doc change.

Let me know if I need to do anything else. Thanks!