main() -> main(void) & fix spacing in c.html.markdown

c.html.markdown

@@ -55,7 +55,7 @@ int add_two_ints(int x1, int x2); // function prototype
 
 // Your program's entry point is a function called
 // main with an integer return type.
-int main() {
+int main(void) {
   // print output using printf, for "print formatted"
   // %d is an integer, \n is a newline
   printf("%d\n", 0); // => Prints 0