fix: Replace deprecated syntax

As of sphinx-design 0.8.0 the "^^^" and "+++" syntax are deprecated.

See https://sphinx-design.readthedocs.io/en/latest/cards.html#legacy-separator-syntax

Author: AlexanderWells-diamond

docs/index.md

@@ -22,7 +22,7 @@ top bar.
 :maxdepth: 2
 tutorials
 ```
-+++
+:::{card-footer}
 Tutorials for installation and typical usage. New users start here.
 :::
 
@@ -31,7 +31,7 @@ Tutorials for installation and typical usage. New users start here.
 :maxdepth: 2
 how-to
 ```
-+++
+:::{card-footer}
 Practical step-by-step guides for the more experienced user.
 :::
 
@@ -40,7 +40,7 @@ Practical step-by-step guides for the more experienced user.
 :maxdepth: 2
 explanations
 ```
-+++
+:::{card-footer}
 Explanations of how it works and why it works that way.
 :::
 
@@ -49,7 +49,7 @@ Explanations of how it works and why it works that way.
 :maxdepth: 2
 reference
 ```
-+++
+:::{card-footer}
 Technical reference material including APIs and release notes.
 :::