[JOSS] Add description for non-specialist audience

[yongrenjie]

(This issue is opened as part of @yongrenjie and @llewelld's review of the Journal of Open Source Software submission, 'Powering single-cell analyses in the browser with WebAssembly'.)

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The summary gives a clear idea about the scientific area the tool works in and its particular benefits (those being 'omics and in-browser client-side operation). These are great points that the text is clear on. However, in terms of a clear description for a "diverse, non-specialist audience", we feel a little more detail would be helpful, in particular explaining what some of the consequences (scientific outputs) of using the software might allow, since this helps put the software in a context that's easier for non-specialists to grasp. For example: "This tool allows variations between cells in a population to be studied, in order to understand how biochemical diversity underlies and gives rise to physiological processes".

[LTLA]

Added a few more sentences about what people usually try to get out of single-cell analyses in kanaverse/kana-paper#6.

[llewelld]

Thanks for the additions. These changes look good to me, but I'd defer to @yongrenjie for his opinion on this too.

[yongrenjie]

Looks good!