Suggestion for cross OS

[irfandyj]

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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