[export] Improve root-sequence help messages #2414

Job	Run time
test (python=3.8 biopython=1.80)	9m 20s
test (python=3.8 biopython=latest)	9m 13s
pathogen-repo-ci (avian-flu)	1m 21s
test (python=3.9 biopython=1.80)	8m 59s
test (python=3.9 biopython=latest)	9m 15s
pathogen-repo-ci (ebola)	1m 37s
test (python=3.10 biopython=1.80)	9m 22s
pathogen-repo-ci (lassa)	1m 24s
test (python=3.10 biopython=latest)	9m 27s
pathogen-repo-ci (mumps)	1m 34s
test (python=3.11 biopython=1.80)	9m 32s
pathogen-repo-ci (ncov)	1m 35s
test (python=3.11 biopython=latest)	9m 23s
pathogen-repo-ci (rsv)	2m 55s
pathogen-repo-ci (seasonal-flu)	1m 34s
pathogen-repo-ci (tb)	1m 57s
build-docs / build-conda	0s
build-docs / build-pip	50s
codecov	15s
	1h 29m 33s

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