docs: Add troubleshooting entry for TLS issue on Android 7.0.
docs: Add troubleshooting entry for TLS issue on Android 7.0.

Learned this thanks to a user report and some debugging:
  https://chat.zulip.org/#narrow/stream/48-mobile/near/782174

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