run-bench is not working and not documented

[glesur]

the script run-bench doesn't work: on Jean Zay:

./run-bench run --gpu v100 --idefix-tag v2.2.00 --account xxxxx --max-cores 64
...
From https://github.com/kokkos/kokkos
 * branch                09e775bfc585840bb9ab1156cbd8d7d1c9e0cc6d -> FETCH_HEAD
Submodule path 'src/kokkos': checked out '09e775bfc585840bb9ab1156cbd8d7d1c9e0cc6d'
cp: cannot stat 'benchmarks/scripts/OrszagTang3D/setup/*': No such file or directory

In addition, no documentation is available, making the thing cumbersome to use

[lih]

The error is "normal". The script is meant to be run from the root of the repository, as "scripts/run-bench ...". Otherwise, it will not be able to find the benchmark setup files in OrszagTang3D/setup.

I corrected the behaviour in the lastest commit on the run-bench branch, and added a little doc about the script in the README (in the same branch).