docs: 更新 mkdocs.yml 文件，新增 KaTeX 支持

- 在 extra_javascript 中新增了 assets/js/katex.js，以支持数学公式的渲染。

Author: XiaoLFeng

docs/assets/js/katex.js

@@ -0,0 +1,10 @@
+document$.subscribe(({ body }) => { 
+    renderMathInElement(body, {
+      delimiters: [
+        { left: "$$",  right: "$$",  display: true },
+        { left: "$",   right: "$",   display: false },
+        { left: "\\(", right: "\\)", display: false },
+        { left: "\\[", right: "\\]", display: true }
+      ],
+    })
+  })

mkdocs.yml

@@ -66,4 +66,5 @@ plugins:
   - search
   - mermaid2
 extra_javascript:
-  - assets/js/extra.js
+  - assets/js/extra.js
+  - assets/js/katex.js