Add a description for the `velocity_pivot` parameter #14782

Job	Run time
📊 Static checks / Code style, file formatting, and docs	38s
🍏 iOS / Template (target=template_release)	3m 15s
🤖 Android / Template (target=template_release)	5m 24s
🍎 macOS / Editor (target=editor, tests=yes)	6m 2s
🐧 Linux / Editor w/ Mono (target=editor)	4m 42s
🍎 macOS / Template (target=template_release)	3m 53s
🌐 Web / Template (target=template_release)	1m 44s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)	14m 39s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	9m 42s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	12m 43s
🏁 Windows / Editor (target=editor, tests=yes)	12m 26s
🐧 Linux / Template w/ Mono (target=template_release)	2m 58s
🏁 Windows / Template (target=template_release)	10m 44s
🐧 Linux / Minimal template (target=template_release, everything disabled)	1m 34s
🪲 Godot CPP / Build and test Godot CPP	6m 53s
	1h 37m 17s

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