Fixed readme heuristic

[ntlhui]

Allowing additional dataset scope files.

[a8ghosh]

The edits do what they're supposed to, but I'm not entirely convinced it's a good idea. Having multiple readmes would make it confusing for people looking at the data later on. It might be worth asking/requiring uploaders to add descriptions on their file names if it's a separate extension. Opening up a dataset and seeing 'readme.md, readme.pptx, readme.png' would be confusing after all.

On the other hand, if the descriptions were there, it could be systemOutline.png and MathworksSymposiumPresentationSP23.pptx. The naming conventions could be hammered out later on, and we can still require them to name files using "readme-FileDescription-.ext", but I think it could be a worthwhile change to make. Though if this isn't a requirement we want to make, then I can approve the PR.