Add "How to cite"

README.md

@@ -7,6 +7,7 @@
 [![codecov](https://codecov.io/gh/OverLordGoldDragon/ssqueezepy/branch/master/graph/badge.svg?token=8L7YPN5N19)](https://codecov.io/gh/OverLordGoldDragon/ssqueezepy)
 [![PyPI version](https://badge.fury.io/py/ssqueezepy.svg)](https://badge.fury.io/py/ssqueezepy)
 [![Codacy Badge](https://app.codacy.com/project/badge/Grade/7cee422639034bcebe0f10ca4b95a506)](https://www.codacy.com/gh/OverLordGoldDragon/ssqueezepy/dashboard?utm_source=github.com&utm_medium=referral&utm_content=OverLordGoldDragon/ssqueezepy&utm_campaign=Badge_Grade)
+[![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.5080508.svg)](https://doi.org/10.5281/zenodo.5080508)
 [![License: MIT](https://img.shields.io/badge/License-MIT-green.svg)](https://opensource.org/licenses/MIT)
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@@ -157,6 +158,23 @@ The Discrete Fourier Transform lays the foundation of signal processing with rea
 
  - [David Bondesson](https://github.com/DavidBondesson): ridge extraction (`ridge_extraction.py`; `examples/`: `extracting_ridges.py`, `ridge_extraction/README.md`)
 
+## How to cite
+
+Short form:
+
+> OverLordGoldDragon, ssqueezepy, 2020. GitHub repository, https://github.com/OverLordGoldDragon/ssqueezepy/. DOI: 10.5281/zenodo.5080508
+
+BibTeX:
+
+```bibtex
+@article{OverLordGoldDragon2020ssqueezepy,
+  title={ssqueezepy},
+  author={OverLordGoldDragon},
+  journal={GitHub. Note: https://github.com/OverLordGoldDragon/ssqueezepy/},
+  year={2020},
+  doi={10.5281/zenodo.5080508},
+}
+```
 
 ## References