Fixes and prep for installing from branch

[zduvall]

Update README, add script for building/pushing to a build branch, and fix event object undefined bug.

See this PR for details on undefined event bug:

jaredpalmer#4029

[github-actions]

Size Change: +19 B (+0.05%)

Total Size: 40.7 kB

Filename	Size	Change
packages/formik/dist/formik.cjs.development.js	16.3 kB	+7 B (+0.04%)
packages/formik/dist/formik.cjs.production.min.js	7.12 kB	+5 B (+0.07%)
packages/formik/dist/formik.esm.js	16.2 kB	+7 B (+0.04%)

ℹ️ View Unchanged

Filename	Size
packages/formik-native/dist/formik-native.cjs.development.js	305 B
packages/formik-native/dist/formik-native.cjs.production.min.js	241 B
packages/formik-native/dist/formik-native.esm.js	239 B
packages/formik-native/dist/index.js	146 B
packages/formik/dist/index.js	141 B

_{compressed-size-action}