diff --git a/README.md b/README.md
index f2be7ba..09be3be 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,10 @@ Then install this repo as a package:
 pip install -e .
 ```
 
+If you want to be able to use full / contextual covariances, install with the optional dependency 'pca':
+```bash
+pip install -e '.[pca]'
+```
 ## Usage
 
 ### TRPL