Fix missing environment template reference in root README

[observerr411]

• Location: README.md:79
• Problem: Setup instructs users to copy .env.example, but .env.example is not present in repository root.
• Resolution criteria: Add .env.example or update README to remove/replace that step.

[njohnchi]

@njohnchi has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I would like to work on this please

ℹ️ Repo Maintainers: To accept this application, review their application or assign @njohnchi to this issue.