docs: fix docker compose quick start

[quantumsheep]

There were missing files (E.g. .env.example, nginx directory, etc...). Cloning the repository prevents such issues.

[vercel[bot]]

@quantumsheep is attempting to deploy a commit to the Plane Team on Vercel.

A member of the Team first needs to authorize it.

[pablohashescobar]

Hi @quantumsheep, thank you for your valuable contribution. We greatly appreciate your effort, and we are pleased to inform you that your contribution has been successfully merged.