branch doc: update description for `--list`

branch doc: update description for `--list`

The paragraph begins with a sample command line `git branch <name>`
that has nothing to do with the option being described.  Remove it,
but use the space to instead show that multiple patterns can be
given.

Also mention the unfortunate `-l` that can be easily confused with
it.

Signed-off-by: Junio C Hamano <redacted>
Reviewed-by: Jonathan Nieder <redacted>
Reviewed-by: Ævar Arnfjörð Bjarmason <redacted>
Signed-off-by: Junio C Hamano <redacted>