Update loading.mdx to include "jsonl" file loading.
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6647). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update. > Thanks for adding the explicit loading command.
> 
> However, I would move it just below, where we present the JSON-Lines example.
> 
> * Maybe adding that this format is called JSON-Lines
> * Add the example after the JSON-Lines data example
> 
> https://github.com/huggingface/datasets/blob/14d9afbb7ae1b787c450261ca0ff374551993031/docs/source/loading.mdx#L135-L138

Thank you @albertvillanova for the feedback! I moved the jsonl file loading example to a more appropriate location. 
* A small update to the documentation, noting the ability to load jsonl files. 