add testPyPI installation

Author: delipouya

README.md

@@ -17,6 +17,12 @@ Single-cell RNA sequencing (scRNA-seq) maps gene expression heterogeneity within
 Please make sure to install the following packages **before installing sciRED**:
 numpy, pandas, scanpy, statsmodels, seaborn, [umap-learn](https://pypi.org/project/umap-learn/), matplotlib, scikit-learn, scipy, xgboost, scikit-image, [diptest==0.2.0](https://pypi.org/project/diptest/0.2.0/)
 
+sciRED package can be installed using PyPI:
+
+```bash
+pip install -i https://test.pypi.org/simple/ sciRED
+```
+
 
 ## Tutorial