Clarify the instructions for using the .env file

[mathewhodson]

This fixes #7950.

The previous text didn't give clear guidance if you were using Windows.

[hamishwillee]

FWIW I like this more in some ways and less in others. This won't work on the Windows command prompt for example.

To me the important bit is actually the file. How you get there is a detail. So how about something like?

---

6. Next, you'll want to start the local preview service, so you can see the changes you'll make as they would look in production:

   # Switch to a separate terminal.
   cd ~/repos/mdn/content
   yarn
   yarn start

   After running the commands above, you can view your local version of the site in any browser at the URL: http://localhost:5000.

7. When browsing a page locally you can press the Open in your editor button to start editing the current page.

   To specify VS Code as your preferred editor create a file named .env in the root of your local content directory that contains the following line:

   EDITOR=code

   • You can create this file from the bash or Windows Powershell terminal using the command echo 'EDITOR=code' >> .env.
   • EDITOR is an environment variable. You can set it to any editor you like using the normal mechanism for your operating system/terminal (i.e. you don't have to use the .env file or VS Code).

[hamishwillee]

Thanks very much!