Suggestion for cross OS

[jippy89]

Please use this template to help contributors get a detailed description of the issue or feature.

For support questions, please use stackoverflow. This repository's issues are reserved for feature requests and bug reports.

1. Apply either the bug or feature-request label

feature-request

2. Describe the bug or feature

This suggestion comes from an issue that I faced on #531.

I tried replacing the npm variables in examples/package.json with the real value and it worked!
Now, this is just a suggestion, maybe instead of using the npm variables we'll just use the real value for cross OS compatibility? Or perhaps, add a documentation about it somewhere in the README.md.

I don't mind creating a PR for both solutions.

3. If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

Nope.

4. Please tell us about your environment:

System:
    OS: Windows 10 10.0.22000
    CPU: (12) x64 11th Gen Intel(R) Core(TM) i7-11600H @ 2.90GHz
  Binaries:
    Node: 16.13.2 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.17 - C:\Program Files\nodejs\yarn.CMD
    npm: 8.1.2 - C:\Program Files\nodejs\npm.CMD
  Languages:
    Python: 3.9.10 - /c/Users/Jip Irfandy/AppData/Local/Programs/Python/Python39/python
  Browsers:
    Edge: Spartan (44.22000.120.0), Chromium (101.0.1210.39)
  npmGlobalPackages:
    gatsby-cli: 4.16.0