Move `optimize_for_size` paragraph up #122

Job	Run time
no_std (ubuntu-latest, stable)	11s
Default (ubuntu-latest, stable)	12s
no_std (ubuntu-latest, nightly)	14s
build-std (build_std)	39s
Default (ubuntu-latest, nightly)	14s
no_std (macos-latest, stable)	17s
Default (macos-latest, stable)	18s
build-std (no_main/nix)	42s
no_std (macos-latest, nightly)	19s
Default (macos-latest, nightly)	16s
no_main-win (stable)	40s
Default (windows-latest, stable)	44s
no_main-win (nightly)	30s
no_std-win (stable)	52s
Default (windows-latest, nightly)	41s
no_std-win (nightly)	29s
	7m 18s

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