Update README

[hieutbui]

Summary

This pull request includes significant updates to the README.md file to provide more detailed instructions for setting up and running the application. The most important changes include the addition of sections for Flutter installation, Supabase setup, Mapbox integration, and build instructions for different environments.

New setup instructions:

• Added a section for Flutter installation with a link to the official documentation and commands to get all pubspecs and generate needed files.
• Added detailed instructions for setting up a Supabase project, including creating enumerated types and adding necessary SQL functions.
• Included steps to create and store Mapbox map tiles and integrate with CARTO.

Build instructions:

• Provided commands to build the app in both debug and release modes, including setting up environment variables.
• Added a table listing required environment variables and their descriptions for running the system.

[github-actions]

This PR has been deployed to https://hieutbui.github.io/ecoparking_flutter/88