Minor fixes in 1990/tbr

Remove note in Makefile that this entry does not compile with modern
compilers. I fixed that quite a while ago but neglected to remove the
message.

The README.md I changed 'i/o' to 'I/O' and I removed the reference to
the original version with gets() from the archive as it's now in the
tbr.orig.c file.

1990/tbr/Makefile

@@ -130,7 +130,6 @@ all: data ${TARGET}
 	supernova deep_magic magic charon pluto
 
 ${PROG}: ${PROG}.c
-	@echo "NOTE: This entry might not compile when using modern compilers."
 	${CC} ${CFLAGS} $< -o $@ ${LDFLAGS}
 
 # alternative executable