Fix branch name from jellyfish to koi in the document of koi release

Fix branch name from jellyfish to koi in the document of koi release

When the agl developer create agl source tree of koi release using repo,
they create jellyfish source tree.  Because the document of koi has incorrect
description for repo command example.
This patch fix to this issue.

Signed-off-by: Naoto YAMAGUCHI <i33399_YAMAGUCHI@aisin-aw.co.jp>
Change-Id: I0b7d3fe76c38383eed291bd1c78c74bf20c998ca
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/26179
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>