message: Update dataset information in README.md
diff: @@ -99,8 +99,7 @@ Configuration file should be a json format file e.g. [simple_sparse_embedding.js
  There are four sessions in a configuration file: "solver", "optimizer", "data", "layers". The sequence of these sessions is not restricted.
  * You can specify the device (or devices), batchsize, model_file.. in `solver` session;
  * and the `optimizer` that will be used in every layer.
  -* File list and data set related configurations will be specified under `data` session.
  -* Finally, layers should be listed under `layers`. Note that embedders should always be the first layer.
  +* Finally, layers should be listed under `layers`. Note that embedders should always be the first layers.
  ### Model File ###
  Model file is a binary file that will be loaded for weight initilization.
  @@ -130,18 +129,24 @@ A data file (binary) contains a header and data (many samples).
  Header Definition:
  ```c
  typedef struct DataSetHeader_ {
  + long long error_check; //0: no error check; 1: check_num
  long long number_of_records; // the number of samples in this data file
  long long label_dim; // dimension of label
  - long long slot_num; //the number of slots in each sample
  - long long reserved; //reserved for future use
  + long long dense_dim; //dimension of dense feature
  + long long slot_num; //slot_num for each embedding
  + long long reserved[3]; // reserved for future use
  } DataSetHeader;
  +
  ```
  Data Definition (each sample):
  ```c
  typedef struct Data_{
  - int label[label_dim];
  + int length; //bytes in this sample (optional: only in check_sum mode )
  + float label[label_dim];
  + float dense[dense_dim];
  Slot slots[slot_num];
  + char checkbits; //checkbit for this sample (optional: only in checksum mode)
  } Data;
  typedef struct Slot_{
  