Updates to 1993/cmills - alt code + bugs + format

The README.md file has been format/typo checked.

The alt version uses usleep(3) with a configurable time (at compile
time). This version is suggested first as it apparently goes too fast in
modern systems. I say apparently as it doesn't appear to work with
macOS. I don't know if it works in other platforms but it is in bugs.md,
that there is a problem.

1993/cmills/Makefile

@@ -57,11 +57,11 @@ ARCH=
 
 # Defines that are needed to compile
 #
-CDEFINE=
+CDEFINE= -DZ=100
 
 # Include files that are needed to compile
 #
-CINCLUDE= -I ${X11_INCDIR} -I ${X11_INCDIR}/X11
+CINCLUDE= -I ${X11_INCDIR} -I ${X11_INCDIR}/X11 -include unistd.h
 
 # Optimization
 #
@@ -113,8 +113,8 @@ OBJ= ${PROG}.o
 DATA=
 TARGET= ${PROG}
 #
-ALT_OBJ=
-ALT_TARGET=
+ALT_OBJ= ${PROG}.alt.o
+ALT_TARGET= ${PROG}.alt
 
 
 #################
@@ -141,6 +141,9 @@ chris: ${PROG}
 alt: data ${ALT_TARGET}
 	@${TRUE}
 
+${PROG}: ${PROG}.c
+	${CC} ${CFLAGS} $< -o $@ ${LDFLAGS}
+
 # data files
 #
 data: ${DATA}