Update docs/Advanced-Usage/DTM-Debugging.rst

Co-Authored-By: Jerry Zhao <jerryz123@berkeley.edu>

docs/Advanced-Usage/DTM-Debugging.rst

@@ -3,6 +3,8 @@ Debugging with DTM/JTAG
 
 By default, Chipyard is not setup to use the Debug Test Module (DTM) to bringup the core.
 Instead, Chipyard uses TSI commands to bringup the core (which normally results in a faster simulation).
+TSI simulations use the SimSerial interface to directly write the test binary into memory, while the DTM 
+executes a small loop of code to write the test binary byte-wise into memory.
 However, if you want to use JTAG, you must do the following steps to setup a DTM enabled system.
 
 Creating a DTM/JTAG Config