docs: add plugin setup guide

plugin/lib/commonlibf4/include/RE/L/LEVELED_OBJECT.h

@@ -0,0 +1,18 @@
+#pragma once
+
+namespace RE
+{
+	class ContainerItemExtra;
+
+	class LEVELED_OBJECT
+	{
+	public:
+		// members
+		TESForm*            form;        // 00
+		ContainerItemExtra* itemExtra;   // 08
+		std::uint16_t       count;       // 10
+		std::uint16_t       level;       // 12
+		std::int8_t         chanceNone;  // 14
+	};
+	static_assert(sizeof(LEVELED_OBJECT) == 0x18);
+}