ENH: Add config for pre-commit

[charlesdong1991]

this is just a draft which kind of shows what i wanna say for #755

i set it to WIP, so feel free to comment and i will change. @ueshin @HyukjinKwon

[codecov-io]

Codecov Report

Merging #756 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #756   +/-   ##
=======================================
  Coverage   93.91%   93.91%           
=======================================
  Files          32       32           
  Lines        5667     5667           
=======================================
  Hits         5322     5322           
  Misses        345      345

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[charlesdong1991]

ahh, just checked .travis.yml, and find out it's building py35, but black only runs on py36 or newer, so pip install will fail..

[ueshin]

Maybe we don't need to add it as a dependency, but in that case, definitely we have to add some instruction to install the library for contributors.

[charlesdong1991]

yeah, agree... have to remove it, i will add some instructions in CONTRIBUTING.md.

[ueshin]

nit: add a line break at the end of a file.

[charlesdong1991]

thanks, added!
i also notice line length used in koalas is 100, not 88 when reading through contributing.md, also changed in this file.

[HyukjinKwon]

To me, I'm okie. Seems worth trying.