pkb: add scimark2 + its license to README.md's benchmarks
pkb: add scimark2 + its license to README.md's benchmarks

Also fix some formatting inconsistencies for surrounding benchmarks in the list.

GoogleCloudPlatform/PerfKitBenchmarker,gablg1/PerfKitBenchmarker,gablg1/PerfKitBenchmarker,tvansteenburgh/PerfKitBenchmarker,juju-solutions/PerfKitBenchmarker,AdamIsrael/PerfKitBenchmarker,AdamIsrael/PerfKitBenchmarker,meteorfox/PerfKitBenchmarker,emaeliena/PerfKitBenchmarker,syed/PerfKitBenchmarker,emaeliena/PerfKitBenchmarker,msurovcak/PerfKitBenchmarker,meteorfox/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,tvansteenburgh/PerfKitBenchmarker,kivio/PerfKitBenchmarker,askdaddy/PerfKitBenchmarker,syed/PerfKitBenchmarker,lleszczu/PerfKitBenchmarker,ksasi/PerfKitBenchmarker,mateusz-blaszkowski/PerfKitBenchmarker,mateusz-blaszkowski/PerfKitBenchmarker,juju-solutions/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,lleszczu/PerfKitBenchmarker,msurovcak/PerfKitBenchmarker,ksasi/PerfKitBenchmarker,askdaddy/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,kivio/PerfKitBenchmarker