docs: add plugin setup guide

plugin/lib/commonlibf4/include/RE/A/ArrowProjectile.h

@@ -0,0 +1,19 @@
+#pragma once
+
+#include "RE/M/MissileProjectile.h"
+
+namespace RE
+{
+	class __declspec(novtable) ArrowProjectile :
+		public MissileProjectile  // 000
+	{
+	public:
+		static constexpr auto RTTI{ RTTI::ArrowProjectile };
+		static constexpr auto VTABLE{ VTABLE::ArrowProjectile };
+		static constexpr auto FORM_ID{ ENUM_FORM_ID::kPARW };
+
+		// members
+		AlchemyItem* poison;  // 2C0
+	};
+	static_assert(sizeof(ArrowProjectile) == 0x2D0);
+}