docs: add plugin setup guide

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

@@ -0,0 +1,19 @@
+#pragma once
+
+#include "RE/B/BSTArray.h"
+
+namespace RE
+{
+	class DECAL_CREATION_DATA;
+
+	class BGSDecalGroup
+	{
+	public:
+		// members
+		bool                           permanentGroup;  // 00
+		bool                           manualSaveLoad;  // 01
+		BSTArray<std::uint32_t>        decalGroup;      // 08
+		BSTArray<DECAL_CREATION_DATA*> pendingDecals;   // 20
+	};
+	static_assert(sizeof(BGSDecalGroup) == 0x38);
+}