Update README.md

Author: alahiff

examples/SU2/README.md

@@ -16,8 +16,14 @@ Download and install the appropriate version of SU2, e.g. on Linux:
 wget https://github.com/su2code/SU2/releases/download/v7.0.2/SU2-v7.0.2-linux64-mpi.zip
 unzip SU2-v7.0.2-linux64-mpi.zip
 ```
-Download the required files:
+Ensure that the environment variable `SU2_RUN` in the `SU2.sh` script is set to the `bin` directory created above.
+
+Download the required config file and mesh file:
 ```
 wget https://raw.githubusercontent.com/su2code/Tutorials/master/compressible_flow/Inviscid_ONERAM6/inv_ONERAM6.cfg
 wget https://github.com/su2code/Tutorials/raw/master/compressible_flow/Inviscid_ONERAM6/mesh_ONERAM6_inv_ffd.su2
 ```
+Execute the script:
+```
+. ./SU2.sh
+```