fix: Mark admonition as containing Markdown, add newlines for readability/parsers

Issue=15: #15

Author: pawamoy

src/griffe2md/templates/docstring/admonition.md.jinja

@@ -1,4 +1,6 @@
-<details class="{{ section.value.kind }}" open>
+<details class="{{ section.value.kind }}" open markdown="1">
 <summary>{{ section.title }}</summary>
+
 {{ section.value.contents }}
-</details>
+
+</details>