README.dev.md: Improve pip instructions.
README.dev.md: Improve pip instructions.

Recommend using a virtualenv.
Add instruction to do `pip install --upgrade pip` before installing
python packages.

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