docs: Clarify who can collaborate in area label teams.
docs: Clarify who can collaborate in area label teams.

Collaboration in area label teams is only available to members of the
Zulip organization on GitHub. For non-members the related links are
not working, which can be confusing.  Address this by explaining the
links won't work and also that anyone can join.

mahim97/zulip,mahim97/zulip,kou/zulip,amanharitsh123/zulip,kou/zulip,dhcrzf/zulip,jackrzhang/zulip,brainwane/zulip,Galexrt/zulip,tommyip/zulip,mahim97/zulip,rishig/zulip,synicalsyntax/zulip,kou/zulip,brockwhittaker/zulip,zulip/zulip,jackrzhang/zulip,andersk/zulip,jackrzhang/zulip,zulip/zulip,showell/zulip,eeshangarg/zulip,Galexrt/zulip,amanharitsh123/zulip,Galexrt/zulip,timabbott/zulip,tommyip/zulip,brainwane/zulip,amanharitsh123/zulip,synicalsyntax/zulip,hackerkid/zulip,synicalsyntax/zulip,punchagan/zulip,jackrzhang/zulip,punchagan/zulip,dhcrzf/zulip,kou/zulip,andersk/zulip,Galexrt/zulip,Galexrt/zulip,hackerkid/zulip,tommyip/zulip,mahim97/zulip,rishig/zulip,rishig/zulip,rht/zulip,andersk/zulip,brainwane/zulip,punchagan/zulip,shubhamdhama/zulip,tommyip/zulip,hackerkid/zulip,jackrzhang/zulip,brockwhittaker/zulip,timabbott/zulip,shubhamdhama/zulip,hackerkid/zulip,eeshangarg/zulip,shubhamdhama/zulip,showell/zulip,rishig/zulip,amanharitsh123/zulip,timabbott/zulip,tommyip/zulip,eeshangarg/zulip,rishig/zulip,mahim97/zulip,punchagan/zulip,timabbott/zulip,hackerkid/zulip,synicalsyntax/zulip,synicalsyntax/zulip,zulip/zulip,rishig/zulip,dhcrzf/zulip,tommyip/zulip,showell/zulip,brockwhittaker/zulip,eeshangarg/zulip,rishig/zulip,hackerkid/zulip,showell/zulip,zulip/zulip,brainwane/zulip,brockwhittaker/zulip,brainwane/zulip,brockwhittaker/zulip,amanharitsh123/zulip,amanharitsh123/zulip,mahim97/zulip,eeshangarg/zulip,jackrzhang/zulip,Galexrt/zulip,brainwane/zulip,timabbott/zulip,rht/zulip,andersk/zulip,brainwane/zulip,hackerkid/zulip,timabbott/zulip,zulip/zulip,jackrzhang/zulip,kou/zulip,kou/zulip,punchagan/zulip,andersk/zulip,zulip/zulip,rht/zulip,dhcrzf/zulip,rht/zulip,Galexrt/zulip,showell/zulip,eeshangarg/zulip,eeshangarg/zulip,punchagan/zulip,dhcrzf/zulip,brockwhittaker/zulip,punchagan/zulip,showell/zulip,andersk/zulip,kou/zulip,showell/zulip,tommyip/zulip,shubhamdhama/zulip,dhcrzf/zulip,timabbott/zulip,synicalsyntax/zulip,andersk/zulip,rht/zulip,zulip/zulip,dhcrzf/zulip,rht/zulip,shubhamdhama/zulip,shubhamdhama/zulip,shubhamdhama/zulip,synicalsyntax/zulip,rht/zulip