📝 added example of how to use the 'getPreviewIcon' prop

src/components/DropzoneArea.md

@@ -21,3 +21,41 @@ import { DropzoneArea } from 'material-ui-dropzone';
   onChange={(files) => console.log('Files:', files)}
 />
 ```
+
+### Custom Preview Icon
+
+Demonstration of how to customize the preview icon for: 
+* PDF files
+* Video
+* Audio
+* Word Documents
+
+
+```jsx
+import react from 'react'
+import { AttachFile, AudioTrack, Description, PictureAsPdf, Theaters } from '@material-ui/icons';
+
+const handlePreviewIcon=(fileObject, classes) => {
+  const {type} = fileObject.file 
+  const iconProps = { className : classes.smallPreviewImg} 
+
+  if (type.startsWith("video/")) return <Theaters {...iconProps} />
+  if (type.startsWith("audio/")) return <AudioTrack {...iconProps} />
+
+  let component
+  switch (type) {
+    case "application/msword": 
+    case "application/vnd.openxmlformats-officedocument.wordprocessingml.document": 
+      return <Description {...iconProps} />      
+    case "application/pdf":
+      return <PictureAsPdf {...iconProps} />  
+    default:
+      return <AttachFile {...iconProps} />  
+  }
+
+}
+
+<DropzoneArea
+  getPreviewIcon={handlePreviewIcon}
+/>
+```