feat(stack): introduce a stack ds, internally this uses a sll

README.md

@@ -45,6 +45,20 @@ ds_hmp_free(&hmp, NULL);
 free(b);
 ```
 
+## Stack
+```c
+char *a = "a";
+char *b = "b";
+
+ds_stack_t *stack = ds_stack_init();
+ds_stack_push(stack, a); // [ "a" ]
+ds_stack_push(stack, b); // [ "b", "a" ]
+ds_stack_peek(stack, 0); // "b"
+ds_stack_pop(stack); // "b"
+ds_stack_pop(stack); // "a"
+free(stack);
+```
+
 # TODO
 - [ ] more data structures
 - [x] tests