Add a Why section to README

[adelbertc]

Inspired by a colleague who had a bit of trouble figuring out what problem Cats was solving

[non]

Looks reasonable to me. 👍

[DavidGregory084]

I think maybe you could expand on the phrase leaving a bit to be desired as this does not seem to describe the problem with these abstractions being absent - maybe something like limiting the level of abstraction and therefore the reusability of code written against the standard library alone?

[ceedubs]

Warning: bike shedding - I'm sorry.

However, common abstractions such as Monoid, Monad, and Traverse are currently missing from the standard library, leaving a bit to be desired.

The word missing here suggests that Monoid etc should be in the standard library, which is an opinion that many may hold, but at the end of the day is an opinion. I'd be inclined to focus on the positive rather than the negative. What do you think of something like the following?

The scala language supports both object-oriented and functional programming, and this is reflected in the hybrid OO/FP approach of its standard library. Cats is an exploration into what the standard library might look like if it focused mostly on functional programming. It takes advantage of scala features such as implicits and higher-kinded types to provide type classes such as Monoid, Monad, and Traverse, which provide composable abstractions for common use-cases. While Cats encourages reuse of some standard library data structures such as List and Option, it also provides some of its own algebraic data types such as Xor and Validated. <Typelevel plug here>

[adelbertc]

@ceedubs Good point, reworded it a bit, lmk what you think

[zmccoy]

Thanks for adding this.

[codecov-io]

Current coverage is 88.80%

Merging #1052 into master will increase coverage by 0.17%

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  Lines          2717       3028   +311   
  Methods        2655       2980   +325   
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+ Hits           2408       2689   +281   
- Misses          309        339    +30   
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[ceedubs]

👍