docs: fix code blocks overflowing and add syntax highlighting

Without these options code blocks would overflow. See:
https://github.com/asiffer/mkdocs-shadcn/issues/57
And it also provides nice syntax highlighting.

docs_requirements.txt

@@ -1,2 +1,3 @@
 mkdocs
 mkdocs-shadcn
+pygments

mkdocs.yml

@@ -6,6 +6,7 @@ markdown_extensions:
   - smarty
   - admonition
   - attr_list
+  - codehilite
 
 theme:
   name: shadcn