Add Repo Badges to README.md

[Nelson]

• Add standard repo badges to the README.md of this repo
• figure out what's going on with Codecov: https://app.codecov.io/gh/dwyl/envar/ 🤷‍♂️ 🔍

https://github.com/dwyl/envar/runs/4930190661?check_suite_focus=true

[Nelson]

Repo activated on Codecov:
https://app.codecov.io/gh/dwyl/envar/branches?page=1&order=-updatestamp

But badge still not working ... 🤷‍♂️

[Nelson]

https://codecov.io/gh/dwyl/envar/branch/main