docs: add plugin setup guide

plugin/lib/commonlibf4/include/RE/H/hknpConstraintId.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "RE/H/hkHandle.h"
+
+namespace RE
+{
+	struct hknpConstraintIdBaseDiscriminant;
+
+	struct hknpConstraintId :
+		public hkHandle<std::uint32_t, 0x7FFF'FFFF, hknpConstraintIdBaseDiscriminant>
+	{};
+	static_assert(sizeof(hknpConstraintId) == 0x4);
+}