Fixes link issue regarding sandbox test PowerShell script (microsoft#146048)

Author: vikingnope

doc/README.md

@@ -37,7 +37,8 @@ For more details, see ["Submit packages to Windows Package Manager"](https://doc
 
 ### In Windows Sandbox
 
-You can use the [Sandbox Test](/Tools/SandboxTest.ps1) PowerShell script for testing a manifest installation in [Windows Sandbox](https://docs.microsoft.com/windows/security/threat-protection/windows-sandbox/windows-sandbox-overview). The manifest will be also validated.
+
+You can use the [Sandbox Test](../Tools/SandboxTest.ps1) PowerShell script for testing a manifest installation in [Windows Sandbox](https://docs.microsoft.com/windows/security/threat-protection/windows-sandbox/windows-sandbox-overview). The manifest will be also validated.
 
 Just provide the path to manifest as parameter: