LinkedList [Ruby]

#### This issue is about [LinkedList](https://en.wikipedia.org/wiki/Linked_list).

- [x] Issue Title is in form `Algo/DS Name [Language]`.
- [x] I searched or browsed the repo’s other issues to ensure this is not a duplicate.
- [x] This Algo/DS is worth adding to this repository.
- [x] Assign this issue to me (I want to work on this).
- [x] I ensure that I am not already assigned to 2 or more issues.
- [x] I will send my PR only after I'm assigned to this issue by any maintainer.
- [x] I understand that I will be unassigned from this issue if I fail to send a PR for this within a week.

Review the existing algorithm and data-structure implementations in the iiitv/algos repository, then compare related issues for the expected contribution pattern. The work is complete when a Ruby LinkedList implementation has been added in the repository's established style.

Written by the indexing model from the issue text.