add instruction to show .env

[itsmarble]

Background

This pull request aims to improve the user experience when configuring API keys in the Auto-GPT project. The changes include clear instructions for accessing hidden files (.env.template) in various operating systems and explaining the rationale behind hiding the file.

Changes

• Updated the configuration instructions to explain how to reveal hidden files in different operating systems.

  Locate the file named .env.template in the main /Auto-GPT folder. This file may be hidden by default in some operating systems due to the dot prefix. To reveal hidden files, follow the instructions for your specific operating system (e.g., in Windows, click on the "View" tab in File Explorer and check the "Hidden items" box; in macOS, press Cmd + Shift + .).

Documentation

The updated instructions are included in the README.md file and the project's main documentation.

Test Plan

PR Quality Checklist

• [x] My pull request is atomic and focuses on a single change.
• [ ] I have thoroughly tested my changes with multiple different prompts.
• [x] I have considered potential risks and mitigations for my changes.
• [x] I have documented my changes clearly and comprehensively.
• [x] I have not snuck in any "extra" small tweaks changes