Add test for markdown footnotes

osu.Game.Tests/Visual/Online/TestSceneWikiMarkdownContainer.cs

@@ -199,6 +199,17 @@ Line after image";
             });
         }
 
+        [Test]
+        public void TestFootnotes()
+        {
+            AddStep("set content", () => markdownContainer.Text = @"This text has a footnote[^test].
+
+Here's some more text[^test2] with another footnote!
+
+[^test]: This is a **footnote**.
+[^test2]: This is another footnote [with a link](https://google.com/)!");
+        }
+
         private partial class TestMarkdownContainer : WikiMarkdownContainer
         {
             public LinkInline Link;