install docs: Cut SSL cert from requirements summary.
install docs: Cut SSL cert from requirements summary.

The summary already has a qualifier that basically says it shouldn't
matter for most people -- making it simultaneously the most
complicated bullet there, and among the least likely to matter.

And in fact, this requirement shouldn't matter for *anyone* when first
experimenting with Zulip.  If certbot won't work in a given admin's
environment, and the available ways to get a cert aren't convenient,
they can always let the installer generate a self-signed cert to get
going, and circle back to the issue later.

So, make that option clear in the main requirements text, and then
just cut the whole bullet from the summary.

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