add post-install tip on how to run `scoop update pwsh` without opening a new powershell.exe window/tab/shell

[wis]

add an additional line to the post-install notes with a tip on how to run scoop update pwsh without opening a new powershell.exe window/tab/shell:

  Since Scoop uses pwsh.exe internally, to update PowerShell Core itself,
  run `scoop update pwsh` from Windows PowerShell, i.e. powershell.exe.
+ You can run the command `powershell.exe -C scoop update pwsh` in any shell prompt, e.g. from WSL.

  Add PowerShell Core as a explorer context menu by running: '$dir\\install-explorer-context.reg'
  For file context menu, run '$dir\\install-file-context.reg'

Relates to #3572

• [x] I have read the Contributing Guide.

[github-actions[bot]]

All changes look good.

Wait for review from human collaborators.

pwsh

• [x] Description
• [x] License
• [x] Hashes
• [x] Checkver
• [x] Autoupdate
• [x] Autoupdate Hash Extraction