docs: add plugin setup guide

plugin/lib/commonlibf4/include/RE/T/TESGrassAreaParam.h

@@ -0,0 +1,13 @@
+#pragma once
+#include "RE/G/GrassParam.h"
+
+namespace RE
+{
+	class TESGrassAreaParam
+	{
+	public:
+		GrassParam grassParam;  // 00
+		float      density[9];  // 28
+	};
+	static_assert(sizeof(TESGrassAreaParam) == 0x50);
+}