Adding README format for Submissions

README_SUBMISSION_TEMPLATE.md

+> Dear participants, for the final due diligence on your submission, please use the below README format to describe your submission. We also encourage you to add useful comments in your code to help streamline the review process.
+
+
+# Submission
+
+## Submission Summary
+
+* Submission ID: XXXXX
+* Submitter: XXXXX
+* Final rank: Xth place on leaderboard X
+* Final scores on MDXDB21:
+
+  | SDR_song | SDR_bass | SDR_drums | SDR_other | SDR_vocals |
+  | :---:    | :---:    | :---:     | :---:     | :---:      |
+  | X.XX     | X.XX     | X.XX      | X.XX      | X.XX       |
+
+## Model Summary
+
+Please describe here your approach, including
+* the model that you used
+  (please cite relevant references, e.g., [1] if you use open-unmix)
+* the training and validation dataset you used
+* hyperparameters that you tuned
+  (e.g., blending strength for system that blends two models)
+
+[1] Stöter, Fabian-Robert, et al. "Open-unmix-a reference implementation for
+    music source separation." Journal of Open Source Software 4.41 (2019): 1667.
+
+
+# Reproduction
+
+## How to reproduce the submission
+
+Please describe here how your submission can be reproduced.
+
+## How to reproduce the training
+
+Please describe here how your model could be trained.