docs: Be explicit about continuing with upgrades.
docs: Be explicit about continuing with upgrades.

Strongly suggest Xenial -> Bionic, or upgrading to 3.x, at the end of
the various other upgrading steps.

zulip/zulip,zulip/zulip,kou/zulip,kou/zulip,kou/zulip,rht/zulip,brainwane/zulip,punchagan/zulip,eeshangarg/zulip,brainwane/zulip,kou/zulip,eeshangarg/zulip,punchagan/zulip,rht/zulip,andersk/zulip,showell/zulip,hackerkid/zulip,eeshangarg/zulip,eeshangarg/zulip,hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,punchagan/zulip,showell/zulip,zulip/zulip,zulip/zulip,zulip/zulip,rht/zulip,punchagan/zulip,hackerkid/zulip,brainwane/zulip,punchagan/zulip,kou/zulip,andersk/zulip,showell/zulip,showell/zulip,brainwane/zulip,brainwane/zulip,rht/zulip,andersk/zulip,showell/zulip,showell/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,kou/zulip,punchagan/zulip,eeshangarg/zulip,andersk/zulip,brainwane/zulip,hackerkid/zulip,brainwane/zulip,kou/zulip,andersk/zulip,andersk/zulip,andersk/zulip,hackerkid/zulip,eeshangarg/zulip,showell/zulip,hackerkid/zulip,rht/zulip