updated readme with new reserved constructor #419

Job	Run time
Build each header individually	1m 0s
build (lpc1756)	15s
build (atsam3x8e)	14s
build (lpc802)	14s
build (lpc1754)	20s
build (lpc1752)	21s
build (atsam4s2b)	15s
build (lpc1759)	15s
build (lpc1788)	16s
build (rp2350)	20s
build (lpc55s66)	20s
build (stm32h723)	20s
build (mb9bf566k)	15s
build (max32625)	19s
build (stm32f103)	20s
build (stm32f407)	14s
build (tmpm373)	14s
build (max32660)	14s
	5m 46s

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