fix/blackpill/readme: Add note about bmputil #93

Job	Run time
build-macos (macos-13)	58s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, 96b_carbon)	34s
build-macos (macos-14)	21s
build-mingw (windows-2022, ucrt64)	1m 57s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, blackpill-f401cc)	34s
build-linux (ubuntu-22.04, jammy, clang-13)	34s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, blackpill-f401ce)	34s
build-linux (ubuntu-22.04, jammy, clang-18)	50s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, blackpill-f411ce)	39s
build-linux (ubuntu-22.04, jammy, gcc-11)	40s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, bluepill)	33s
build-linux (ubuntu-22.04, jammy, gcc-13)	1m 1s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, ctxlink)	38s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, f072)	28s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, f3)	27s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, f4discovery)	27s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, hydrabus)	26s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, launchpad-icdi)	25s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, native)	34s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, native-uncommon)	24s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, native-st-clones)	39s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, native-riscv)	26s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, native-remote)	29s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, stlink)	25s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, stlinkv3)	27s
build-firmware (ubuntu-22.04, jammy, 12.2.Rel1, swlink)	27s
package-firmware	7s
	16m 4s

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