Improve README

[IndrajeetPatil]

Instead of being a feature dump, it should describe the package goals.

When ready, including #87 will also improve things.

[etiennebacher]

Maybe we could replace the list of examples with a two-column table showing data wrangling functions in one column and data transformation functions in the other one?

[IndrajeetPatil]

I was actually thinking that maybe we could just copy-paste most of the content from our JOSS paper. It gives the high-level and overview and also points to a place where all available functionality can be found.

We did the same for see package README. WDYT?

[etiennebacher]

Why not, but I think we can trim the JOSS paper and not copy paste it exactly in the readme. To take the example of see, I think the statement of need could be shortened to a few bullet points. I would prefer having a quick summary of the core use of the package and links to the paper and website. But this is just my preference