benchmarks: add note about specs of machine compiling benchmarks

[skip ci]

scripts/results/README.md

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+These benchmarks results are compiled on my main development machine -
+an Apple Mac Mini 2023 model with an M2 Pro chip with 12 CPU cores and 32GB of RAM;
+a 1TB SSD primary drive and a 1TB Samsung SSD 970 Evo plus external drive
+running MacOS Sonoma Public Beta.
+
+It uses the prebuilt, CPU optimized qsv binary variant in aarch64-apple-darwin.zip
+found at https://github.com/jqnatividad/qsv/releases/latest.