better fileSizeError custom message, updated readme

README.md

@@ -111,7 +111,7 @@ customMessage: PropTypes.shape({
   instructions: PropTypes.string, // default: 'Drag-n-drop a file or click to add an image'
   acceptedFileTypes: PropTypes.string, // default: 'Accepted file types: '
   maxFileSize: PropTypes.string, // default: 'Max file size: '
-  fileTypeErrorMessage: PropTypes.string, // default: `File size must be less than $BYTES`
+  fileTypeErrorMessage: PropTypes.string, // default: 'File size must be less than $BYTES'. maxFileSize value can be referenced with '$BYTES'
   fileSizeErrorMessage: PropTypes.string, // default: 'Invalid file type'
 })
 ```

src/DropNCrop.js

@@ -74,7 +74,7 @@ class DropNCrop extends Component {
       customMessage,
     } = this.props;
     const fileSizeErrorMessage = customMessage.fileSizeErrorMessage 
-      ? customMessage.fileSizeErrorMessage + bytesToSize(maxFileSize) 
+      ? customMessage.fileSizeErrorMessage.replace('$BYTES',bytesToSize(maxFileSize))
       : null;
     const fileSizeValidation = fileSizeLessThan(maxFileSize, fileSizeErrorMessage)(files);
     const fileTypeValidation = fileType(allowedFileTypes, customMessage.fileTypeErrorMessage)(files);