Fix the URL in README.md

The previous URL of The Linux/x86 Boot Protocol returned a 404 error
due to an incorrect origin.
Updated the link to point to the correct resource.

References:
- The Linux/x86 Boot Protocol:
  https://www.kernel.org/doc/html/latest/arch/x86/boot.html

Author: otischung

README.md

@@ -109,7 +109,7 @@ a BSD-style license that can be found in the LICENSE file.
 ## References
 * [kvmtool](https://github.com/kvmtool/kvmtool)
 * [KVM (Kernel-based Virtual Machine) API](https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt)
-* [The Linux/x86 Boot Protocol](https://www.kernel.org/doc/html/latest/x86/boot.html)
+* [The Linux/x86 Boot Protocol](https://www.kernel.org/doc/html/latest/arch/x86/boot.html)
 * [Using the KVM API](https://lwn.net/Articles/658511/)
 * [gokvm](https://github.com/bobuhiro11/gokvm)
 * [KVM Host in a few lines of code](https://zserge.com/posts/kvm/)