Update README.md .env.template instructions

[Explorergt92]

Background

Elaborates on the .env.template renaming process to reduce the number of questions on the discord server pertaining to API key setting and saving the .env file. I found 489 search results in the discord server for '.env'

Changes

5. Rename .env.template to .env and fill in your OPENAI_API_KEY. If you plan to use Speech Mode, fill in your ELEVENLABS_API_KEY as well.

to

5. Locate the file named '.env.template' in the 'Auto-GPT' folder.
   Open the ".env" file in a text editor.
   Find the line that says "OPENAI_API_KEY=".
   After the "=", enter your unique OpenAI API Key (without any quotes or spaces).
   Enter any other API keys or Tokens for services you'd like to utilize.
   Rename this file to ".env" by removing the ".template" extension.
   Use the 'Save as..' option and chose 'No Extension' from the 'Save as type:' dropdown menu below the file name. 
   Save and close the ".env" file.
   By completing these steps, you'll properly configure the API Key for your project.

Documentation

Test Plan

PR Quality Checklist

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