Add Todos documentation

[ci skip]

doc/workflow/README.md

@@ -22,3 +22,4 @@
 - [Merge When Build Succeeds](merge_when_build_succeeds.md)
 - [Manage large binaries with Git LFS](lfs/manage_large_binaries_with_git_lfs.md)
 - [Importing from SVN, GitHub, BitBucket, etc](importing/README.md)
+- [Todos](todos.md)

doc/workflow/todos.md

+# GitLab ToDos
+
+>**Note:** This feature was [introduced][ce-2817] in GitLab 8.5.
+
+When you log into GitLab, you normally want to see where you should spend your
+time and take some action, or what you need to keep an eye on. All without the
+mess of a huge pile of e-mail notifications. GitLab is where you do your work,
+so being able to get started quickly is very important.
+
+Todos is a chronological list of to-dos that are waiting for your input, all
+in a simple dashboard.
+
+![Todos screenshot showing a list of items to check on](img/todos_index.png)
+
+---
+
+You can access quickly your Todos dashboard by clicking the round gray icon
+next to the search bar in the upper right corner.
+
+![Todos icon](img/todos_icon.png)
+
+## What triggers a Todo
+
+A Todo appears in your Todos dashboard when:
+
+- an issue or merge request is assigned to you
+- you are `@mentioned` in an issue or merge request, be it the description of
+  the issue/merge request or in a comment
+
+>**Note:** Commenting on a commit will _not_ trigger a Todo.
+
+## How a Todo is marked as Done
+
+Any action to the corresponding issue or merge request will mark your Todo as
+**Done**. This action can include:
+
+- changing the assignee
+- changing the milestone
+- adding/removing a label
+- commenting on the issue
+
+In case where you think no action is needed, you can manually mark the todo as
+done by clicking the corresponding **Done** button, and it will disappear from
+your Todos list. If you want to mark all your Todos as done, just click on the
+**Mark all as done** button.
+
+---
+
+In order for a Todo to be marked as done, the action must be coming from you.
+So, if you close the related issue or merge the merge request yourself, and you
+had a Todo for that, it will automatically get marked as done. On the other
+hand, if someone else closes, merges or takes action on the issue or merge
+request, your Todo will remain pending. This makes sense because you may need
+to give attention to an issue even if it has been resolved.
+
+There is just one Todo per issue or merge request, so mentioning a user a
+hundred times in an issue will only trigger one Todo.
+
+## Filtering your Todos
+
+In general, there are four kinds of filters you can use on your Todos
+dashboard:
+
+| Filter | Description |
+| ------ | ----------- |
+| Project | Filter by project |
+| Author  | Filter by the author that triggered the Todo |
+| Type    | Filter by issue or merge request |
+| Action  | Filter by the action that triggered the Todo (Assigned or Mentioned)|
+
+You can choose more than one filters at the same time.
+
+[ce-2817]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2817