update README.md

Makefile

+.PHONY: 01 02 all
+
 all:
 	mkdir -p build;
 	cmake -S . -B build;
@@ -15,4 +17,3 @@ all:
 	make -C build;
 	./build/02-jumping-boxes;
 
-.PHONY: 01 02 all

README.md

@@ -11,7 +11,8 @@ make
 
 To build and run a specific game:
 ```
-make 01
+make 01   # To run 01-red-circle
+make 02   # To run 02-jumping-boxes
 ```
 
 _See `Makefile` for complete list of commands_