prod docs: Call out more the need for a chained cert bundle.
prod docs: Call out more the need for a chained cert bundle.

This is kind of easy to gloss over, especially with the framing
as a "format"; surely if things work at all, the file format
must have been right, right?  It's really a bit more substantive
than that; say so and also add a bit more description.

jackrzhang/zulip,andersk/zulip,andersk/zulip,dhcrzf/zulip,kou/zulip,hackerkid/zulip,tommyip/zulip,rht/zulip,hackerkid/zulip,brainwane/zulip,timabbott/zulip,rishig/zulip,synicalsyntax/zulip,punchagan/zulip,synicalsyntax/zulip,jackrzhang/zulip,punchagan/zulip,hackerkid/zulip,jackrzhang/zulip,rishig/zulip,shubhamdhama/zulip,rishig/zulip,punchagan/zulip,brainwane/zulip,timabbott/zulip,hackerkid/zulip,synicalsyntax/zulip,synicalsyntax/zulip,timabbott/zulip,brainwane/zulip,showell/zulip,eeshangarg/zulip,kou/zulip,zulip/zulip,shubhamdhama/zulip,dhcrzf/zulip,tommyip/zulip,rishig/zulip,hackerkid/zulip,andersk/zulip,zulip/zulip,rht/zulip,zulip/zulip,rht/zulip,tommyip/zulip,showell/zulip,punchagan/zulip,dhcrzf/zulip,timabbott/zulip,eeshangarg/zulip,tommyip/zulip,andersk/zulip,brainwane/zulip,showell/zulip,synicalsyntax/zulip,shubhamdhama/zulip,eeshangarg/zulip,zulip/zulip,shubhamdhama/zulip,dhcrzf/zulip,andersk/zulip,rht/zulip,timabbott/zulip,rishig/zulip,eeshangarg/zulip,synicalsyntax/zulip,kou/zulip,kou/zulip,showell/zulip,brainwane/zulip,eeshangarg/zulip,tommyip/zulip,andersk/zulip,dhcrzf/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,zulip/zulip,jackrzhang/zulip,tommyip/zulip,shubhamdhama/zulip,rht/zulip,brainwane/zulip,tommyip/zulip,punchagan/zulip,rht/zulip,timabbott/zulip,jackrzhang/zulip,kou/zulip,kou/zulip,shubhamdhama/zulip,zulip/zulip,rishig/zulip,punchagan/zulip,eeshangarg/zulip,eeshangarg/zulip,jackrzhang/zulip,showell/zulip,rishig/zulip,shubhamdhama/zulip,showell/zulip,hackerkid/zulip,jackrzhang/zulip,brainwane/zulip,andersk/zulip,zulip/zulip,timabbott/zulip,dhcrzf/zulip,showell/zulip,dhcrzf/zulip,synicalsyntax/zulip,rht/zulip