some sh updates

src/001-hello-world/hello-world.sh

@@ -1,2 +1,4 @@
+# To run the program, but the code in `hello-world.go` and
+# use `go run`.
 $ go run hello-world.go
 Hello world

src/003-variables/variables.sh

@@ -1 +1,3 @@
-go run variables.go
+$ go run variables.go
+Hello world
+1 2