Update README.md (#172)

The sycl2020 model variant names needs update with the Babelstream 5.0

Author: kaanolgu

README.md

@@ -102,7 +102,7 @@ The source for each model's implementations are located in `./src/<model>`.
 
 Currently available models are:
 ```
-omp;ocl;std-data;std-indices;std-ranges;hip;cuda;kokkos;sycl;sycl2020;acc;raja;tbb;thrust;futhark
+omp;ocl;std-data;std-indices;std-ranges;hip;cuda;kokkos;sycl;sycl2020-acc;sycl2020-usm;acc;raja;tbb;thrust;futhark
 ```
 
 #### Overriding default flags