docs: add a single-line command to update the PowerShell profile

docs/guides/quick-start.md

@@ -105,21 +105,11 @@ echo 'vfox activate fish | source' >> ~/.config/fish/config.fish
 
 ::: details Powershell
 
-Open PowerShell Profile:
-
 ```shell
-New-Item -Type File -Path $PROFILE # Just ignore the 'file already exists' error.
-
-# If it prompts "Unable to find the path", then you need to forcefully create profile. Add the "-Force" option.
-# New-Item -Type File -Path $PROFILE –Force
-
-Invoke-Item $PROFILE  # open Profile
-```
-
-Add the following line to the end of your profile and save:
+if (-not (Test-Path -Path $PROFILE)) { New-Item -Type File -Path $PROFILE -Force }; Add-Content -Path $PROFILE -Value 'Invoke-Expression "$(vfox activate pwsh)"'
 
-```shell
-Invoke-Expression "$(vfox activate pwsh)"
+# Create profile if it does not exist: New-Item -Type File -Path $PROFILE -Force
+# Add content to profile: Add-Content -Path $PROFILE -Value 'Invoke-Expression "$(vfox activate pwsh)"'
 ```
 
 :::