Doc: cover multiple contains/no-contains filters

Doc: cover multiple contains/no-contains filters

Update documentation for "git branch", "git for-each-ref" and "git tag"
with notes explaining what happens when passed multiple --contains or
--no-contains filters.

This behavior is useful to document prior to enabling multiple
merged/no-merged filters, in order to demonstrate consistent behavior
between merged/no-merged and contains/no-contains filters.

Signed-off-by: Aaron Lipman <alipman88@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>