docs: add plugin setup guide

plugin/lib/commonlibf4/include/RE/B/BSSpring_SpringState.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "RE/N/NiPoint3.h"
+
+namespace RE
+{
+	namespace BSSpring
+	{
+		template <class T>
+		class SpringState
+		{
+		public:
+			// members
+			T     position;        // 00
+			T     velocity;        // ??
+			float springConstant;  // ??
+		};
+
+		extern template class SpringState<float>;
+		extern template class SpringState<NiPoint2>;
+		extern template class SpringState<NiPoint3>;
+	}
+}