Remove reference to windows 7 in self-signed build docs (nvaccess#17192)

The self signed build docs reference Windows 7. Windows 7 is no longer supported in NVDA.

Description of user facing changes
None

Description of development approach
Update docs to remove reference to windows 7 in self-signed build docs

projectDocs/dev/selfSignedBuild.md

@@ -70,9 +70,14 @@ Thumbprint                                Subject
 148CB69869B802A36B3D8D801BA8D9D0F3C1484F  CN=Test NVDA Build, O=NV Access Dev, C=US
 ```
 
-For Windows 7, you will need to use an alternative method.
+#### Note for older versions of Windows
+
 On any supported version of Windows, you can manage certifications through the "Certificate Manager".
 
+Importing A Windows 11 certificate via PowerShell may fail on older versions of Windows.
+On Windows 10, open the certificate file and go through the installation dialog.
+Install it to "Local Machine", in the store: "Trusted Root Certification Authorities".
+
 ### Using the certificate
 
 When running a scons command, append `certFile=local.pfx certPassword=<Password>`.