doc: update flux_reactor_create(3) flags #2520

Job	Run time
spelling	4s
Generate build matrix	8s
validate commits	0s
python linting	30s
bookworm - test-install	7m 40s
bookworm - 32 bit	7m 41s
noble - test-install	7m 38s
el9 - test-install	7m 41s
alpine - test-install	3m 19s
fedora40 - test-install	7m 38s
jammy - test-install	7m 39s
focal - py3.8	7m 39s
bookworm - gcc-12,content-s3,distcheck	7m 38s
fedora40 - clang-18	7m 39s
coverage	7m 40s
el8 - ascii	7m 39s
el8 - test-install	7m 39s
el8 - system,coverage	7m 27s
inception	7m 40s
flux-accounting check	4m 36s
flux-sched check	4m 14s
flux-pam check	4m 1s
macos build only	1m 41s
flux-pmix check	7m 16s
Generate docker manifest	1s
	2h 12m 48s

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