add prettier as dependency and precommit script

[magicznyleszek]

@pmusaraj I already have prettier installed as a plugin in my editor. The plugin has an option to apply prettier on saving file, and it worked great for me since I started using it. Now I see the prettier folk recommend adding a precommit script that prettify staged files - do you think we would like to try that, or better to have some control on the commits?

[pmusaraj]

Yes, let's try the precommit script.

[magicznyleszek]

@pmusaraj I've found out you can have .prettierignore so it will not fix automatically some files (like package.json for example. I've added what I think should be there, but feel free to improve it :)