simple_detector.md: updating for dd4pod to edm4hep

src/docs/part1/simple_detector.md

@@ -181,8 +181,8 @@ This accomplishes the following:
 Later on you can see its use while looping over hits:
 
 ```cpp
-auto pos0 = h.getPosition();
-auto pos1 = cellid_converter.position(h.getCellID());
+auto pos0 = h.position;
+auto pos1 = cellid_converter.position(h.cellID);
 ```
 Here `h` is a [EDM4hep SimTrackerHit](https://edm4hep.web.cern.ch/classedm4hep_1_1_sim_tracker_hit.html) 
 which has `position`, a