In af09ce2 ("sparse-checkout: init and set in cone mode", 2019-11-21),
the '--cone' option was added to 'git sparse-checkout init'.
Document it.
Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>