Add description of "Inherit" blend mode in Spine component

Documentation contains description only for some of the available options for Spine component
https://defold.com/extension-spine/#blend-modes
but "Inherit" mode is missing
<img width="549" height="205" alt="Image" src="https://github.com/user-attachments/assets/666dcd86-2803-474a-965f-70c8f22ad8df" />