Add config file in trade

Update readme in trade
Update highfreq to delete nan order

examples/highfreq/README.md

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+# High-Frequency Dataset
+
+This dataset is an example for RL high frequency trading.
+
+## Get High-Frequency Data
+
+Get high-frequency data by running the following command:
+```bash
+    python workflow.py get_data
+```
+
+## Dump & Reload & Reinitialize the Dataset
+
+
+The High-Frequency Dataset is implemented as `qlib.data.dataset.DatasetH` in the `workflow.py`. `DatatsetH` is the subclass of [`qlib.utils.serial.Serializable`](https://qlib.readthedocs.io/en/latest/advanced/serial.html), whose state can be dumped in or loaded from disk in `pickle` format.
+
+### About Reinitialization
+
+After reloading `Dataset` from disk, `Qlib` also support reinitializing the dataset. It means that users can reset some states of `Dataset` or `DataHandler` such as `instruments`, `start_time`, `end_time` and `segments`, etc.,  and generate new data according to the states.
+
+The example is given in `workflow.py`, users can run the code as follows.
+
+### Run the Code
+
+Run the example by running the following command:
+```bash
+    python workflow.py dump_and_load_dataset
+```