Annotation For Makefile

Origin for each line in Makefile from check-in e90770a5a7:

0a9369ff13 2019-05-02        rkeene: all: example.so
0a9369ff13 2019-05-02        rkeene: 
e90770a5a7 2019-05-02        rkeene: example.c: $(shell find example -type f) $(shell find lib -type f) xvfs.c.rvt xvfs-create Makefile
0a9369ff13 2019-05-02        rkeene: 	./xvfs-create --directory example --name example > example.c.new
0a9369ff13 2019-05-02        rkeene: 	mv example.c.new example.c
0a9369ff13 2019-05-02        rkeene: 
e90770a5a7 2019-05-02        rkeene: example.o: example.c xvfs-core.h Makefile
e90770a5a7 2019-05-02        rkeene: 	cc -Wall -I. -o example.o -c example.c
0a9369ff13 2019-05-02        rkeene: 
e90770a5a7 2019-05-02        rkeene: example.so: example.o Makefile
0a9369ff13 2019-05-02        rkeene: 	cc -shared -o example.so example.o
0a9369ff13 2019-05-02        rkeene: 
0a9369ff13 2019-05-02        rkeene: test:
0a9369ff13 2019-05-02        rkeene: 	@echo not implemented
0a9369ff13 2019-05-02        rkeene: 
0a9369ff13 2019-05-02        rkeene: clean:
0a9369ff13 2019-05-02        rkeene: 	rm -f example.so example.o example.c
0a9369ff13 2019-05-02        rkeene: 
0a9369ff13 2019-05-02        rkeene: distclean: clean
0a9369ff13 2019-05-02        rkeene: 
0a9369ff13 2019-05-02        rkeene: .PHONY: all clean distclean test