SETUP-04 — Write README with setup instructions

[fgorordodev]

Type: Chore
Priority: Low
Phase: Phase 0
Depends on: SETUP-01

Commit Convention:

<type>(<ID>): <short description in imperative mood>

<optional body explaining the "why", not the "what" — the diff already shows the what>

<optional footer: Closes #<issue number>>

Description

Document how to get the project running locally, so a new contributor (or
future you, cloning the template for a new project) can get started without
having to ask.

Acceptance criteria

• Includes prerequisites (SDK version, Docker)
• Includes the command to start the database via docker-compose
• Includes the command to run the Api locally

Definition of Done - DoD

• The code compiles without warnings.
• It meets all the card's acceptance criteria.
• It follows the layering convention (no business logic in the Controller,
  no outward references from the Domain layer, etc.).
• It includes at least one test if the card is a Feature type (unit or integration,
  depending on the layer).
• Error handling uses domain exceptions, not loose try/catch blocks
  manually returning BadRequest.
• No hardcoded secrets, connection strings, or keys in the code.
• Merged into the main branch (or the designated integration branch).
• The commit/PR references the card ID (e.g., "AUTH-02: implement login").