Update Documentation for Strapi Environment Setup

[coderabbitai]

We need to update the project’s documentation to include instructions for configuring the local .env file (e.g., copying .env.example to .env), obtaining and setting the Strapi credentials, and any CMS integration steps.\n\nReferences:\n- Pull Request: https://github.com/kleros/kleros-website-v2/pull/29\n- Comment: https://github.com/kleros/kleros-website-v2/pull/29#discussion_r1897893001\n\nRequested by @Harman-singh-waraich.