Add starter package

Summary:
Adds a new package with typescript set up, to be published to npm.

Followed this as a guideline: https://itnext.io/step-by-step-building-and-publishing-an-npm-typescript-package-44fe7164964c

Reviewed By: passy

Differential Revision: D18244495

fbshipit-source-id: c684f0bb33e61699f605c637186c7a81136a920f

.eslintrc.js

@@ -55,7 +55,7 @@ module.exports = {
   },
   overrides: [
     {
-      files: ['*.tsx'],
+      files: ['*.tsx', '*.ts'],
       parser: '@typescript-eslint/parser',
       rules: {
         'prettier/prettier': [2, {...prettierConfig, parser: 'typescript'}],