Add comment about /json/subscriptions/exists endpoint.
Add comment about /json/subscriptions/exists endpoint.

We should remove this endpoint.  For now I'm just adding
the comment to the code explaining why we should do that.

verma-varsha/zulip,KingxBanana/zulip,christi3k/zulip,timabbott/zulip,punchagan/zulip,arpith/zulip,vaidap/zulip,andersk/zulip,brainwane/zulip,arpith/zulip,Jianchun1/zulip,mahim97/zulip,christi3k/zulip,jackrzhang/zulip,brockwhittaker/zulip,ryanbackman/zulip,hackerkid/zulip,amyliu345/zulip,shubhamdhama/zulip,AZtheAsian/zulip,brainwane/zulip,hackerkid/zulip,j831/zulip,rht/zulip,ryanbackman/zulip,isht3/zulip,TigorC/zulip,synicalsyntax/zulip,brainwane/zulip,andersk/zulip,Juanvulcano/zulip,SmartPeople/zulip,rht/zulip,dhcrzf/zulip,vikas-parashar/zulip,dawran6/zulip,sonali0901/zulip,peguin40/zulip,zulip/zulip,punchagan/zulip,eeshangarg/zulip,zacps/zulip,tommyip/zulip,vabs22/zulip,jrowan/zulip,dawran6/zulip,rht/zulip,amanharitsh123/zulip,calvinleenyc/zulip,zulip/zulip,shubhamdhama/zulip,samatdav/zulip,jackrzhang/zulip,amyliu345/zulip,vabs22/zulip,eeshangarg/zulip,JPJPJPOPOP/zulip,dawran6/zulip,blaze225/zulip,shubhamdhama/zulip,paxapy/zulip,joyhchen/zulip,vabs22/zulip,punchagan/zulip,samatdav/zulip,timabbott/zulip,zulip/zulip,Jianchun1/zulip,vaidap/zulip,niftynei/zulip,isht3/zulip,TigorC/zulip,jainayush975/zulip,jrowan/zulip,sharmaeklavya2/zulip,isht3/zulip,dhcrzf/zulip,jackrzhang/zulip,hackerkid/zulip,vabs22/zulip,ryanbackman/zulip,j831/zulip,tommyip/zulip,brainwane/zulip,zacps/zulip,timabbott/zulip,sup95/zulip,dattatreya303/zulip,shubhamdhama/zulip,showell/zulip,amanharitsh123/zulip,synicalsyntax/zulip,aakash-cr7/zulip,aakash-cr7/zulip,AZtheAsian/zulip,timabbott/zulip,hackerkid/zulip,grave-w-grave/zulip,dattatreya303/zulip,grave-w-grave/zulip,TigorC/zulip,Jianchun1/zulip,Juanvulcano/zulip,jackrzhang/zulip,vabs22/zulip,blaze225/zulip,samatdav/zulip,blaze225/zulip,sharmaeklavya2/zulip,susansls/zulip,susansls/zulip,synicalsyntax/zulip,hackerkid/zulip,AZtheAsian/zulip,sharmaeklavya2/zulip,reyha/zulip,verma-varsha/zulip,eeshangarg/zulip,niftynei/zulip,Galexrt/zulip,blaze225/zulip,christi3k/zulip,sonali0901/zulip,samatdav/zulip,joyhchen/zulip,SmartPeople/zulip,dhcrzf/zulip,verma-varsha/zulip,rishig/zulip,vaidap/zulip,dhcrzf/zulip,cosmicAsymmetry/zulip,susansls/zulip,zulip/zulip,dawran6/zulip,rishig/zulip,amanharitsh123/zulip,arpith/zulip,rht/zulip,eeshangarg/zulip,dattatreya303/zulip,blaze225/zulip,dattatreya303/zulip,KingxBanana/zulip,ryanbackman/zulip,AZtheAsian/zulip,SmartPeople/zulip,andersk/zulip,calvinleenyc/zulip,dawran6/zulip,KingxBanana/zulip,synicalsyntax/zulip,peguin40/zulip,sonali0901/zulip,souravbadami/zulip,kou/zulip,tommyip/zulip,shubhamdhama/zulip,shubhamdhama/zulip,souravbadami/zulip,zulip/zulip,cosmicAsymmetry/zulip,cosmicAsymmetry/zulip,isht3/zulip,peguin40/zulip,Juanvulcano/zulip,rishig/zulip,rht/zulip,PhilSk/zulip,brockwhittaker/zulip,Diptanshu8/zulip,zulip/zulip,jrowan/zulip,brockwhittaker/zulip,vaidap/zulip,punchagan/zulip,Jianchun1/zulip,showell/zulip,aakash-cr7/zulip,sonali0901/zulip,susansls/zulip,amyliu345/zulip,showell/zulip,dattatreya303/zulip,JPJPJPOPOP/zulip,showell/zulip,brockwhittaker/zulip,rht/zulip,jphilipsen05/zulip,zacps/zulip,brainwane/zulip,kou/zulip,reyha/zulip,calvinleenyc/zulip,jphilipsen05/zulip,souravbadami/zulip,timabbott/zulip,verma-varsha/zulip,reyha/zulip,cosmicAsymmetry/zulip,jrowan/zulip,timabbott/zulip,j831/zulip,mahim97/zulip,rishig/zulip,sharmaeklavya2/zulip,sup95/zulip,jackrzhang/zulip,vikas-parashar/zulip,niftynei/zulip,ryanbackman/zulip,calvinleenyc/zulip,showell/zulip,jphilipsen05/zulip,reyha/zulip,jainayush975/zulip,souravbadami/zulip,Galexrt/zulip,amanharitsh123/zulip,shubhamdhama/zulip,sup95/zulip,blaze225/zulip,PhilSk/zulip,showell/zulip,KingxBanana/zulip,rishig/zulip,mahim97/zulip,JPJPJPOPOP/zulip,Juanvulcano/zulip,zacps/zulip,vikas-parashar/zulip,jainayush975/zulip,jphilipsen05/zulip,calvinleenyc/zulip,j831/zulip,KingxBanana/zulip,christi3k/zulip,vaidap/zulip,kou/zulip,niftynei/zulip,andersk/zulip,sup95/zulip,ryanbackman/zulip,j831/zulip,SmartPeople/zulip,brainwane/zulip,souravbadami/zulip,amyliu345/zulip,KingxBanana/zulip,verma-varsha/zulip,Galexrt/zulip,Galexrt/zulip,sonali0901/zulip,Galexrt/zulip,JPJPJPOPOP/zulip,SmartPeople/zulip,sup95/zulip,mahim97/zulip,joyhchen/zulip,synicalsyntax/zulip,joyhchen/zulip,aakash-cr7/zulip,Diptanshu8/zulip,arpith/zulip,brainwane/zulip,amyliu345/zulip,paxapy/zulip,jainayush975/zulip,calvinleenyc/zulip,vikas-parashar/zulip,cosmicAsymmetry/zulip,paxapy/zulip,jainayush975/zulip,mahim97/zulip,jphilipsen05/zulip,eeshangarg/zulip,dattatreya303/zulip,punchagan/zulip,Jianchun1/zulip,Galexrt/zulip,verma-varsha/zulip,hackerkid/zulip,jrowan/zulip,jainayush975/zulip,amanharitsh123/zulip,PhilSk/zulip,tommyip/zulip,sharmaeklavya2/zulip,paxapy/zulip,andersk/zulip,grave-w-grave/zulip,brockwhittaker/zulip,reyha/zulip,samatdav/zulip,sonali0901/zulip,arpith/zulip,andersk/zulip,Juanvulcano/zulip,kou/zulip,vikas-parashar/zulip,jackrzhang/zulip,Jianchun1/zulip,zacps/zulip,paxapy/zulip,vabs22/zulip,PhilSk/zulip,dhcrzf/zulip,grave-w-grave/zulip,tommyip/zulip,j831/zulip,Diptanshu8/zulip,grave-w-grave/zulip,peguin40/zulip,peguin40/zulip,grave-w-grave/zulip,Diptanshu8/zulip,eeshangarg/zulip,isht3/zulip,jphilipsen05/zulip,andersk/zulip,AZtheAsian/zulip,Galexrt/zulip,sharmaeklavya2/zulip,vikas-parashar/zulip,jrowan/zulip,Juanvulcano/zulip,PhilSk/zulip,kou/zulip,TigorC/zulip,cosmicAsymmetry/zulip,TigorC/zulip,susansls/zulip,eeshangarg/zulip,JPJPJPOPOP/zulip,JPJPJPOPOP/zulip,peguin40/zulip,AZtheAsian/zulip,rishig/zulip,joyhchen/zulip,dhcrzf/zulip,kou/zulip,joyhchen/zulip,Diptanshu8/zulip,timabbott/zulip,paxapy/zulip,sup95/zulip,aakash-cr7/zulip,punchagan/zulip,christi3k/zulip,synicalsyntax/zulip,zulip/zulip,TigorC/zulip,amyliu345/zulip,hackerkid/zulip,isht3/zulip,christi3k/zulip,PhilSk/zulip,rishig/zulip,mahim97/zulip,tommyip/zulip,jackrzhang/zulip,susansls/zulip,niftynei/zulip,rht/zulip,souravbadami/zulip,dawran6/zulip,zacps/zulip,punchagan/zulip,kou/zulip,aakash-cr7/zulip,samatdav/zulip,SmartPeople/zulip,Diptanshu8/zulip,niftynei/zulip,showell/zulip,arpith/zulip,synicalsyntax/zulip,reyha/zulip,amanharitsh123/zulip,tommyip/zulip,vaidap/zulip,dhcrzf/zulip,brockwhittaker/zulip