Update README.md

Author: luglilab

README.md

@@ -55,6 +55,7 @@ Tested on computer with ios 10.15.7
 conda env create -n cytophenograph3 -f ./Cytophenograph/environment_cytophenograph3_mac.yml
 conda activate cytophenograph3
 pip install -e ./Cytophenograph/FlowSOM_LugliLab
+pip install -U PhenoGraph
 ```
 **Strategy 2 : Execute the following command** 
 ```python