add contributors image (#23)

ISSUE #

Closes #23

Added the contributors image.

[X] My code follows the code style of this project.
[X] I have performed a self-review of my own code.
[X] My change requires a change to the documentation.
[X] I have updated the documentation accordingly.
[X] I have read the CONTRIBUTING document.
[X] I have commented my code, particularly in hard-to-understand areas.
[X] My changes generate no new warnings.
[X] I have added tests that prove my fix is effective or that my feature works.
[X] The title of my pull request is a short description of the requested changes.

V2dha / alphadoc