docs: fix typo in getting started guide #26

Job	Run time
ash-ci / mix deps.get	16s
ash-ci / MIX_ENV=dev mix.compile	1m 8s
ash-ci / mix hex.audit	15s
ash-ci / MIX_ENV=test mix.compile	1m 23s
ash-ci / mix spark.formatter --check	5s
ash-ci / mix format --check-formatted	1m 17s
ash-ci / mix sobelow	1m 22s
ash-ci / mix spark.cheat_sheets --check	1m 10s
ash-ci / mix credo --strict	6s
ash-ci / mix deps.unlock --check-unused	1m 6s
ash-ci / mix dialyzer	5m 44s
ash-ci / mix test	1m 46s
ash-ci / Release	0s
	15m 38s

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