Nmap devguide needs updated approaches for detecting installed Npcap version

The Npcap Reference Guide's section on Developing software with Npcap suggests using GetDllVersion on NPFInstall.exe to determine what version is installed on a given machine. I've heard that GetDllVersion may no longer be supported for this, and it's not really the best approach anyway. The document already covers getting the version at runtime by actually linking to the DLL and querying at runtime with pcap_lib_version(). But without going that far, the best approach is probably to grab it from the registry. It's in the DisplayVersion value in the HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\NpcapInst key. Here's one way you could retrieve that on the command-line:

reg.exe query /reg:32 HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\NpcapInst /v DisplayVersion

We should update the Npcap Reference Guide accordingly. If anyone has better suggestions/advice for retrieving this registry info on Windows, please post.

Start with the Npcap Reference Guide's “Developing software with Npcap” section linked in the issue and review its current GetDllVersion guidance. Verify the suggested DisplayVersion registry query, then update the section with the recommended approach while preserving the existing pcap_lib_version() runtime guidance; done means the guide accurately explains how to retrieve the installed version without linking to the DLL.