der: note `no_alloc` in docs (#2207) #3368

Job	Run time
test (i686-unknown-linux-gnu, 1.85.0, sudo apt update && sudo apt install gcc-multilib)	3m 57s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	3m 25s
build (1.85.0, thumbv7em-none-eabi)	35s
test (x86_64-unknown-linux-gnu, 1.85.0)	3m 35s
build (1.85.0, wasm32-unknown-unknown)	28s
build (stable, wasm32-unknown-unknown)	46s
minimal-versions / minimal-versions	49s
test (x86_64-unknown-linux-gnu, stable)	3m 24s
build (stable, thumbv7em-none-eabi)	17s
	17m 16s

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