minor edits to classroom instructions

learn-silice/classroom/soc_wave_player/README.md

@@ -72,7 +72,7 @@ the RISC-V processor.
 The firmware is compiled and embedded when building with `make`.
 To change the firmware source use
 `make stepN FIRMWARE=<src>` where `<src>` is the name of a firmware file
-(without extension) in the subdirectory `firmware`.
+(*without extension*) in the subdirectory `firmware`.
 For instance, to build step 0 with the firmware `firmware/step0_leds.c` use the command: `make step0 FIRMWARE=step0_leds`
 
 > All files `step*.c` or `test*.c`  in `firmware` can be used to generate a firmware. A file prefixed with `step` is meant to be used during the classroom,
@@ -236,7 +236,7 @@ it with the firmware of step 4 ([step4_list_files.c](firmware/step4_list_files.c
 ### Step 5
 
 Encode a music, copy it onto the SDcard and listen to it with the design produced
-by `make step5 FIRMWARE=step5_audio_stream.c`. The music will be recognizable but
+by `make step5 FIRMWARE=step5_audio_stream`. The music will be recognizable but
 the quality will be horrendous.
 
 > The music file should be called `music.raw` and place on the SDcard root directory. Prepare the file using `./encode_music.sh <file.mp3>` (ffmpeg has to be installed). Use your favorite `mp3` (or perhaps not, this music is going to go through a grinder ;) ).
@@ -256,7 +256,7 @@ take only a few lines. Tip: all that is needed is a counter and a comparison.
 
 ### Final
 
-Want to see/hear the end result? `make final FIRMWARE=step5_audio_stream.c`
+Want to see/hear the end result? `make final FIRMWARE=step5_audio_stream`
 
 ### About image files