Update readme

Author: javh

README.rst

@@ -16,9 +16,13 @@ Documentation
 Tutorials and API documentation can be found at:
 https://genentech.github.io/scimilarity/index.html
 
-Download
+Download & Install
 --------------------------------------------------------------------------------
 
+The latest API release can be installed from PyPI::
+
+    pip install scimilarity
+
 Pretrained model weights, embeddings, kNN graphs, a single-cell metadata
 can be downloaded from:
 https://zenodo.org/records/10685499