Update README.md

Author: aayusharyan

README.md

@@ -103,6 +103,7 @@ Available configuration options are:
 function, it will be passed a FlowFile, a FlowChunk and isTest boolean (Default: `/`)
 * `singleFile` Enable single file upload. Once one file is uploaded, second file will overtake existing one, first one will be canceled. (Default: false)
 * `chunkSize` The size in bytes of each uploaded chunk of data. The last uploaded chunk will be at least this size and up to two the size, see [Issue #51](https://github.com/23/resumable.js/issues/51) for details and reasons. (Default: `1*1024*1024`)
+* `calculateChunkSize` Optional function to set chunk size for each file. When this method is defined, chunkSize value will not be considered. File Object will be passed to it and it should return the size (in bytes) of chunks for that file.
 * `forceChunkSize` Force all chunks to be less or equal than chunkSize. Otherwise, the last chunk will be greater than or equal to `chunkSize`. (Default: `false`)
 * `simultaneousUploads` Number of simultaneous uploads (Default: `3`)
 * `fileParameterName` The name of the multipart POST parameter to use for the file chunk  (Default: `file`)