Cannot install created module

[stevstrong]

Hello,
I followed your online course on Youtube and tried to make the steps indicated there.
I have locally installed ODOO 14.
I have checked out this repository branch 14, commit 3d0a7d7 into the folder "C:\dev\Odoo\server\odoo\addons\plant_nursery".
This is the file structure:

I launched ODOO and did find the new app, but when I tried to install it I got the following error message:
"User error:
You try to install module 'plant_nursery' that depends on module 'documents'.
But the latter module is not available in your system."

See attached picture.

What do I miss here?
How can I install the module error free?