onboarding.py: Add link to getting-your-organization-started-with-zulip.
onboarding.py: Add link to getting-your-organization-started-with-zulip.

Also has a few minor updates to the rest of the text.

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