docs: Add nginx reload documentation.
docs: Add nginx reload documentation.

This adds reference for reloading nginx when the certificates are
replaced so that the server works with the new certificates instead of
the old ones.

Fixes: #4849.

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