doc: clarify description of 'submodule.recurse'

doc: clarify description of 'submodule.recurse'

The doc for 'submodule.recurse' starts with "Specifies if commands
recurse into submodles by default". This is not exactly true of all
commands that have a '--recurse-submodules' option. For example, 'git
pull --recurse-submodules' does not run 'git pull' in each submodule,
but rather runs 'git submodule update --recursive' so that the submodule
working trees after the pull matches the commits recorded in the
superproject.

Clarify that by just saying that it enables '--recurse-submodules'.

Note that the way this setting interacts with 'fetch.recurseSubmodules'
and 'push.recurseSubmodules', which can have other values than true or
false, is already documented since 4da9e99e6e (doc: be more precise on
(fetch|push).recurseSubmodules, 2020-04-06).

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>