Add comment to example build.gradle explaining sim GUI config

Related to wpilibsuite/allwpilib#6204

example_projects/wpilib_build_file/build.gradle

@@ -106,7 +106,13 @@ test {
 }
 
 // Simulation configuration (e.g. environment variables).
+//
+// The sim GUI is *disabled* by default to support running
+// AdvantageKit log replay from the command line. Uncomment
+// the second line to *enable* the sim GUI by default (this
+// is the standard WPILib behavior).
 wpi.sim.addGui()
+// wpi.sim.addGui().defaultEnabled = true
 wpi.sim.addDriverstation()
 
 // Setting up my Jar File. In this case, adding all libraries into the main jar ('fat jar')