Fix eessi spelling

Author: jsteyn

miniHPC_step_by_step.md

@@ -92,11 +92,11 @@ ff02::2		ip6-allrouters
 ```
 
 
-- Install ESSI
+- Install EESSI
 
 ```
-mkdir essi
-cd essi
+mkdir eessi
+cd eessi
 wget https://raw.githubusercontent.com/EESSI/eessi-demo/main/scripts/install_cvmfs_eessi.sh
 sudo bash ./install_cvmfs_eessi.sh
 echo "source /cvmfs/software.eessi.io/versions/2023.06/init/bash" | sudo tee -a /etc/profile