__init__.py file inside the folder, eg:
__init__.py does not exist, Anki will ignore the folder.
When choosing a folder name, it is recommended to stick to a-z and 0-9
characters to avoid problems with Python’s module system.
While you can use whatever folder name you wish for folders you create
yourself, when you download an add-on from AnkiWeb, Anki will use the
item’s ID as the folder name, such as: