docs: add plugin setup guide

plugin/lib/commonlibf4/include/RE/N/NiFrustum.h

@@ -0,0 +1,17 @@
+#pragma once
+
+namespace RE
+{
+	class NiFrustum
+	{
+	public:
+		float left;    // 00
+		float right;   // 04
+		float top;     // 08
+		float bottom;  // 0C
+		float near;    // 10
+		float far;     // 14
+		bool  ortho;   // 18
+	};
+	static_assert(sizeof(NiFrustum) == 0x1C);
+}