docs: add plugin setup guide

plugin/lib/commonlibf4/include/RE/F/FUNCTION_DATA.h

@@ -0,0 +1,15 @@
+#pragma once
+
+namespace RE
+{
+	enum class SCRIPT_OUTPUT;
+
+	class FUNCTION_DATA
+	{
+	public:
+		// members
+		REX::TEnumSet<SCRIPT_OUTPUT, std::uint16_t> function;  // 00
+		void*                                       param[2];  // 08
+	};
+	static_assert(sizeof(FUNCTION_DATA) == 0x18);
+}