docs: add plugin setup guide

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

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "RE/M/MemoryManager.h"
+
+namespace RE
+{
+	namespace BSStorageDefs
+	{
+		enum class ErrorCode;
+		enum class SeekMode;
+
+		class StreamBuffer
+		{
+		public:
+			// members
+			std::size_t                    size;    // 00
+			MemoryManager::AutoScrapBuffer buffer;  // 08
+			void*                          ptrCur;  // 10
+		};
+		static_assert(sizeof(StreamBuffer) == 0x18);
+	}
+}