Update README.md to mention creation/activation of conda

Summary: Verified by Shayne

Reviewed By: amirafzali

Differential Revision: D75013277

fbshipit-source-id: 350b6d876b80a5f9a68be5d66315beafc6f48de1

Author: dcci

README.md

@@ -6,6 +6,10 @@ TODO improve
 
 ```sh
 
+# Create and activate the conda environment
+conda create -n monarchenv python=3.10 -y
+conda activate monarchenv
+
 # Install nightly rust toolchain
 curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh