docs: add comments, move sleep() arg to #define

main.c

@@ -1,8 +1,13 @@
+#define SLEEP_SECONDS 20
+
 #include <unistd.h>
 
 int main() {
   while (1) {
-    sleep(20);
+    sleep(SLEEP_SECONDS);
+    // fd 1 = stdout fd number
+    //  "*" = symbol to print
+    //    1 = size of a string to print
     write(1, "*", 1);
   }
   return 0;