book3: Add include hittable_list.h to pdf.h

hollasch · hollasch · commit 6290db051a7a · 2021-08-17T01:48:53.000-07:00
diff --git a/books/RayTracingTheRestOfYourLife.html b/books/RayTracingTheRestOfYourLife.html
@@ -2543,6 +2543,9 @@
 Now we can try sampling directions toward a `hittable`, like the light.
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
+    ...
+    #include "hittable_list.h"
+    ...
     class hittable_pdf : public pdf {
       public:
         hittable_pdf(const hittable_list& _objects, const point3& _origin)
