Add checklists for contributors

Description

Hi there, I'm Gitlab contributor.

I think that Gitlab's support for community is great because of:

• these guides
• several blog posts for contributors
  • https://about.gitlab.com/2016/06/16/fearless-contribution-a-guide-for-first-timers/
  • https://about.gitlab.com/2016/12/07/heres-how-new-programmers-can-learn-by-contributing-to-gitlab/
  • and others ...
• many-many more about what I don't know

At first time I found that contribution process isn't so straightforward for me. We have many possibilities for contribution, but having many choices are bad for humans (I think that we can have for first-timers sort of paradox of choice https://en.wikipedia.org/wiki/The_Paradox_of_Choice).

Now I plan my work, improving the level of contribution (at first it was just doc typo fix, then it was helper's bug fix, then class refactoring, now it's a small feature). For this purpose I use my todo-software, but I think that we can introduce this progress tracking for anyone - with simple checklists (e.g. "checklist for beginner", "My first Merge Request" etc.).

Proposal

1. Make process of individual contribution easier with some sort of contributor's checklists. It can be introduced just now with existing functional of Gitlab:

• create separate project like this sample project https://gitlab.com/innerwhisper/contributors-den
• for checklists we can use separate issues (one per contributor) - https://gitlab.com/innerwhisper/contributors-den/issues
• all checklist templates are just issue templates - https://gitlab.com/innerwhisper/contributors-den/tree/master/.gitlab/issue_templates

1. Add necessary links to [Contributing guide] - https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md
2. Make this lists optional parts of hiring process

P.S. sample project just a sample 😸

Links / references