Update Readme.md

Author: aayusharyan

README.md

@@ -120,6 +120,7 @@ function, it will be passed a FlowFile, a FlowChunk and isTest boolean (Default:
 * `prioritizeFirstAndLastChunk` Prioritize first and last chunks of all files. This can be handy if you can determine if a file is valid for your service from only the first or last chunk. For example, photo or video meta data is usually located in the first part of a file, making it easy to test support from only the first chunk. (Default: `false`)
 * `testChunks` Make a GET request to the server for each chunks to see if it already exists. If implemented on the server-side, this will allow for upload resumes even after a browser crash or even a computer restart. (Default: `true`)
 * `preprocess` Optional function to process each chunk before testing & sending. To the function it will be passed the chunk as parameter, and should call the `preprocessFinished` method on the chunk when finished. (Default: `null`)
+* `changeRawDataBeforeSend` Optional function to change Raw Data just before the XHR Request can be sent for each chunk. To the function, it will be passed the chunk and the data as a Parameter. Return the data which will be then sent to the XHR request without further modification. (Default: `null`). This is helpful when using FlowJS with [Google Cloud Storage](https://cloud.google.com/storage/docs/json_api/v1/how-tos/multipart-upload). Usage example can be seen [#276](https://github.com/flowjs/flow.js/pull/276). (For more, check issue [#170](https://github.com/flowjs/flow.js/issues/170)).
 * `initFileFn` Optional function to initialize the fileObject. To the function it will be passed a FlowFile and a FlowChunk arguments.
 * `readFileFn` Optional function wrapping reading operation from the original file. To the function it will be passed the FlowFile, the startByte and endByte, the fileType and the FlowChunk.
 * `generateUniqueIdentifier` Override the function that generates unique identifiers for each file. (Default: `null`)