makefiles/vars.inc.mk: document PROGRAMMER_QUIET variable

makefiles/vars.inc.mk

@@ -107,6 +107,10 @@ export HEXFILE               # The 'intel hex' stripped result of the compilatio
 # RESET_FLAGS                # The parameters to supply to RESET.
 # PROGRAMMER                 # The programmer to use when flashing, resetting or debugging
 # PROGRAMMERS_SUPPORTED      # The list of programmers supported by a board
+# PROGRAMMER_QUIET           # Change verbosity of programmer output (only used with flash and reset targets).
+                             # Default is 1, not verbose. Use 0 to get normal programmer output.
+# USE_PROGRAMMER_WRAPPER_SCRIPT     # Use the programmer wrapper Python script. Default is 1 (0 if RIOT_CI_BUILD is set).
+
 
 export DLCACHE               # directory used to cache http downloads
 export DOWNLOAD_TO_FILE      # Use `$(DOWNLOAD_TO_FILE) $(DESTINATION) $(URL)` to download `$(URL)` to `$(DESTINATION)`.