create remark plugin

apps/app/src/services/renderer/remark-plugins/mermaid.ts

@@ -0,0 +1,24 @@
+import { fromMarkdown } from 'mdast-util-from-markdown';
+import { Plugin } from 'unified';
+import { Node } from 'unist';
+import { visit } from 'unist-util-visit';
+
+function rewriteNode(node: Node) {
+  const mermaidTree = fromMarkdown(node.value as string);
+
+  // replace node
+  if (mermaidTree.children[0] != null) {
+    node.type = 'paragraph';
+    node.children = mermaidTree.children[0].children;
+  }
+}
+
+export const remarkPlugin: Plugin = function() {
+  return (tree) => {
+    visit(tree, (node) => {
+      if (node.type === 'code' && node.lang === 'mermaid') {
+        rewriteNode(node);
+      }
+    });
+  };
+};