Markdown typesetting

No5: Linked list
README.md

Definition Double Linked List
list arrangement not normal

```md
**Additions**
- `add`: grow the list by adding items to the end of the list.
**Removals**
- `remove`: will always remove from a given position in the list.
**Search**
- `contains`: will search the list for a value.
**Display**
- `display`: displays the complete list in a forward manner.
```