Add Workbench to Addon Manager

Introduction
These are step-by-step instructions on how to add a Python workbench to the Addon Manager.

Requirements:
 * A local git repository.
 * A remote git repository. Supported git hosts are GitHub, GitLab, Framagit and Debian Salsa.
 * Git must be installed.

Enable developer mode

 * 1) Open the Preferences Editor: select the  option from the menu.
 * 2) Select the  option in the left bar.
 * 3) On the  tab check the  checkbox. This will enable the  button in the Addon Manager.
 * 4) Press the  button to close the Preferences Editor.

Create the package.xml file

 * 1) Open the Addon Manager: select the  option from the menu.
 * 2) Press the  button.
 * 3) The  dialog opens. [[Image:Addon_Manager_Addon_Developer_Tools_Dialog.png|350px]]
 * 4) Enter the following:
 * : The path to the local git repository.
 * : This will appear in the listings of the Addon Manager.
 * : Idem.
 * : Idem.
 * : Recommended.
 * : The icon must be part of the repository.
 * 1) Press the  button at the bottom of the dialog.
 * 2) The  dialog opens. [[Image:Addon_Manager_Content_Item_Dialog.png|350px]]
 * 3) The  should be set to.
 * 4) Check the  checkbox.
 * 5) Enter the . This is the class name specified in the  file.
 * 6) For the  enter.
 * 7) Press the  button to close the dialog.
 * 8) Press the  button to close the  dialog and save the  file.
 * 9) Press the  button to close the Addon Manager.
 * 10) Push the created file to your remote repository.
 * 1) Press the  button to close the Addon Manager.
 * 2) Push the created file to your remote repository.

Add the workbench to the .gitmodules file

 * 1) Fork https://github.com/FreeCAD/FreeCAD-addons.
 * 2) Create a new branch.
 * 3) Edit the  file to include your new Addon, in alphabetical order.
 * 4) Push the new branch to GitHub.
 * 5) Submit a Pull Request to the FreeCAD-Addons repository with the new  file.