Update README.md

Author: inokawa

README.md

@@ -99,6 +99,19 @@ const processor = unified()
   .use(docx, { plugins: [imagePlugin()] });
 ```
 
+When we embed `svg` to docx, it also requires `png` image for compatibility reason. On browser, this plugin generate it automatically. On other enviroment like Node.js, please implement `fallbackSvg` prop.
+
+```javascript
+import sharp from "sharp";
+
+imagePlugin({
+  fallbackSvg: async ({ buffer }) => {
+    const png = await sharp(buffer).png().toBuffer();
+    return png.buffer;
+  },
+});
+```
+
 ### Code
 
 Syntax highlighting with [shiki](https://github.com/shikijs/shiki).

src/plugins/image/index.ts

@@ -79,7 +79,7 @@ type SvgToPngFn = (options: {
   buffer: ArrayBuffer;
   width: number;
   height: number;
-}) => Promise<ArrayBuffer>;
+}) => Promise<ArrayBufferLike>;
 
 const loadWithFetch: LoadFn = async (url) => {
   const res = await fetch(url);
@@ -182,7 +182,7 @@ export const imagePlugin = ({
                     width,
                     height,
                     data,
-                    fallback: fallback,
+                    fallback: fallback as ArrayBuffer,
                   });
                 } catch (e) {
                   warnOnce(`Failed to create fallback image: ${url} ${e}`);