Update documentation and do some basic housekeeping

Makefile

@@ -62,7 +62,7 @@ flash: $(TARGET)
 	       -c $(ASP) -p $(ARCH)  \
 	       -U lfuse:w:0xff:m     \
 	       -U hfuse:w:0x91:m     \
-	       -U flash:w:$(TARGET)
+	       -U flash:w:$<
 
 .PHONY: clean
 clean:
@@ -85,6 +85,11 @@ listen: ./opt/tools/serial-listen.py
 	$(E) "[PY3] $<"
 	$(Q) ./$<
 
+.PHONY: listen-web
+listen-web: ./opt/webgui/Makefile
+	$(E) "[MAK] $(<D)"
+	$(Q) $(MAKE) -sC $(<D)
+
 $(TMPDIRS):
 	$(E) "[DIR] $@"
 	$(Q) $(MKDIR) $@