Update GitHub token instructions in README #407

Job	Run time
build-core / Cancel superseded	5s
build-docs / Cancel superseded	5s
build-extras / Cancel superseded	5s
build-docs / Build tsbrowse stable docs	8s
build-docs / Build msprime stable docs	27s
build-docs / Build tstrait stable docs	10s
build-docs / Build msprime latest docs	14s
build-docs / Build tsinfer latest docs	8s
build-docs / Build tskit stable docs	15s
build-docs / Build tstrait latest docs	17s
build-docs / Build tsinfer stable docs	14s
build-docs / Build tsdate stable docs	9s
build-docs / Build tsbrowse latest docs	8s
build-docs / Build tscompare stable docs	8s
build-docs / Build tszip stable docs	12s
build-docs / Build tsdate latest docs	12s
build-docs / Build tscompare latest docs	11s
build-docs / Build sc2ts latest docs	11s
build-docs / Build kastore stable docs	12s
build-docs / Build kastore latest docs	8s
build-docs / Build pyslim stable docs	14s
build-docs / Build pyslim latest docs	10s
build-docs / Build tszip latest docs	11s
build-docs / Build sc2ts stable docs	14s
build-docs / Build tskit latest docs	15s
build-core / Build core site	2m 23s
build-extras / Import tutorials	10s
build-extras / Import rust tutorials	4s
build-extras / Build tskit-explore JupyterLite site	15s
Deploy 🚀 (if on main branch)	32s
	8m 7s

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