docs: Add guides, update READMEs (target#9)

* Changes from old repo

* adding screenshot

* tweak to project description

* Simplify dev setup documentation

* resetdb: don't err if db doesn't exist

* Cleanup contributing guidelines a bit

* Update smoketest readme

* add Dockerfile

* getting started guide

* dev setup guide

* add mailgun section

* add note about API-only mode

* attempt to start postgres container on failure (fix dev issue)

* shorten getting started intro

* tweaks to postgres getting started info

* add link to effective Go in CONTRIBUTING.md

* add links to more info for tests

* add go unit test example

* update label query in README

Co-Authored-By: Mitch Cimenski <[email protected]>
Co-Authored-By: Arundhati Rao <[email protected]>