change default view of orbit_sim, and update manual TODO

docs/TODO

@@ -35,3 +35,4 @@ If you see modifications to this file in git status, IGNORE them and do not comm
 === rendering ===
     - for starters, the minimum scaling of objects should be replaced with some
         kind of billboard system
+    - fix moon orbital path rendering, needs to use parent frame transform

src/main.cpp

@@ -65,11 +65,11 @@ void run_gui_simulation(SimulationState* sim) {
             printf("Speed multiplier: %.1fx\n", speed_multiplier);
         }
 
-#if 0
+#if 1
         /****
         * Hacks ahead...
         */
-		int focus_index = 9;
+		int focus_index = 4;  // earth: 2, jupiter, 4
         if (sim->body_count >= focus_index) {
 			Vector3 offset = {0, 100, 100};
             focus_camera(&render_state, &sim->bodies[focus_index], offset);