ti84: adapt recipe to single stage xcomp

recipes/ti84/Makefile

@@ -1,4 +1,4 @@
-TARGET = stage1.bin
+TARGET = os.bin
 BASEDIR = ../..
 FDIR = $(BASEDIR)/forth
 EDIR = $(BASEDIR)/emul

recipes/ti84/README.md

@@ -38,7 +38,7 @@ screen as output and its builtin keyboard as input.
 
 ## Build the ROM
 
-Running `make` will result in `stage1.rom` being created.
+Running `make` will result in `os.rom` being created.
 
 ## Emulate