Create .env.sample File to Model Dev Environment Variable Setup

[DBNess]

Description
As a follow-up to #315 Use dotenv, let's create a .env.sample file in the root directory to make the development environment setup instructions even more clear for new contributors.

Ask
Create a .env.sample file, with appropriately named GitHub environment variables and fake keys.

To Do

• Add a .env.sample file with example environment variables

Additional Info
dotenv documentation: https://github.com/bkeepers/dotenv