chore(prettier): add .prettierrc file

[with-heart]

This change adds a .prettierrc file to the project.

From looking at the existing code and #8, the current style seems to match prettier defaults except for trailingComma which is set to "all". By specifying only that override, prettier will respect its default values for all other rules.

This allows plugin:prettier/recommended to know what to recommend, and prevents anyone with a global .prettierrc in their local env (like me 😁) from constantly overwriting the expected style.

[CLAassistant]

All committers have signed the CLA.

[nihaals]

I haven't yet looked at prettier's config much as I've been working on actually writing components but this should be a great first change as we decide on style later on. Right now everything's been done just with VSCode's prettier and all default config (afaik).

[nihaals]

Thanks!

[with-heart]

Yeap, just noticed that this should actually be all defaults and trailingComma shouldn't have a custom value. Will fix to just stick with the defaults in a bit :)