Add .prettierrc config file

[wanecek]

Summary

What

Add .prettierrc config file to allow editors to pick up the same settings as those defined in .eslintrc.js

Why

I managed to autoformat the files incorrectly a few times when working on #9. Was a bit annoying, maybe this can help someone in the future :)

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've written tests to cover the new code and functionality included in this PR.
• I've read, agree to, and signed the Contributor License Agreement (CLA).

Not sure what tests to write to cover this. IMO it isn't necessary since we have eslint rules to enforce the rules :)
Couldn't access the CLA agreement found on cla-assistant.io :/

[codecov-io]

Codecov Report

Merging #10 into master will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@ ## master #10 +/- ## ===================================== Coverage 100% 100% ===================================== Files 2 2 Lines 117 117 Branches 5 5 ===================================== Hits 117 117

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[AnujRNair]

Thanks for adding!

[CLAassistant]

All committers have signed the CLA.