docs: Correct details about mobile and desktop codebases.
docs: Correct details about mobile and desktop codebases.

http://zulip.readthedocs.io/en/latest/architecture-overview.html
mentions "Our mobile clients are separate code repositories: Android
and React Native iOS app. " However Zulip Mobile is the official
mobile Zulip client supporting both iOS and Android.

Edited by tabbott to also fix confusion about the desktop.

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