docs: add plugin setup guide

plugin/lib/commonlibf4/include/RE/U/UnloadedRefData.h

@@ -0,0 +1,14 @@
+#pragma once
+
+namespace RE
+{
+	class UnloadedRefData
+	{
+	public:
+		// members
+		std::uint32_t refID;          // 0
+		std::uint32_t parentSpaceID;  // 4
+		std::uint32_t cellKey;        // 8
+	};
+	static_assert(sizeof(UnloadedRefData) == 0xC);
+}