This blogpost will explain how to show/hide workflows in the sidekick.
When you open the sidekick and go to the workflow tab you see a number of default workflows you can use.
To add your own workflow to that list you have to edit the properties of your workflow and add the tags workflow:wcm as shown below.
Don't forget to hit the 'save' button after clicking ok on the page-properties of the workflow.
When you now go to the sidekick you will see you newly added workflow in the list.
NOTE: The hide your workflow from the list in the sidekick you have to remove the workflow:wcm tag *and* replace this with another tag. When you have no tags defined on your workflow it will also show in the list.