feat: add logo to README and docs site

Author: athammad

README.md

@@ -1,3 +1,7 @@
+<p align="center">
+  <img src="docs/assets/logo.png" alt="OnlineCML" width="300"/>
+</p>
+
 > Causal inference for the real world — one observation at a time.
 
 [![CI](https://github.com/athammad/onlinecml/actions/workflows/ci.yml/badge.svg)](https://github.com/athammad/onlinecml/actions/workflows/ci.yml)

docs/assets/logo.png

@@ -6,6 +6,8 @@ repo_name: athammad/onlinecml
 
 theme:
   name: material
+  logo: assets/logo_small.png
+  favicon: assets/logo_small.png
   palette:
     - scheme: default
       primary: indigo