Update README with instructions to activate IRON env (#1931)

Co-authored-by: AndraBisca <[email protected]>
Co-authored-by: Joseph Melber <[email protected]>

Author: 3 people

README.md

@@ -190,6 +190,7 @@ Turn off SecureBoot (Allows for unsigned drivers to be installed):
 >   source yourVitisSetupScript.sh
 >   export LM_LICENSE_FILE=/opt/Xilinx.lic
 >   source /opt/xilinx/xrt/setup.sh
+>   source ironenv/bin/activate
 >   source utils/env_setup.sh my_install/mlir_aie my_install/mlir my_install/llvm-aie
 > ```