README not up to date for standalone benchmark

[leggerf]

for what concerns running benchmarks standalone, looks like executable is missing:

/Users/admin/Code/_/phoronix-converted/phoronix-astcenc-1.0.1 > ls
total 64
0 drwxr-xr-x 10 admin staff 320B Jun 14 16:09 ./
0 drwxr-xr-x 4 admin staff 128B Jun 14 16:09 ../
8 -rw-r--r-- 1 admin staff 698B Jun 14 16:09 benchmark.json
8 -rwxr--r-- 1 admin staff 323B Jun 14 16:03 install.sh*
8 -rwxr--r-- 1 admin staff 280B Jun 14 16:03 install_macosx.sh*
8 -rwxr--r-- 1 admin staff 282B Jun 14 16:03 install_windows.sh*
8 -rw-r--r-- 1 admin staff 1.1K Jun 14 16:09 packages.json
16 -rwxr-xr-x 1 admin staff 6.1K Jun 14 16:09 phoronix_downloader.py*
0 drwxr-xr-x 6 admin staff 192B Jun 14 16:09 presets/
8 -rwxr--r-- 1 admin staff 90B Jun 14 16:09 setup.sh*