DOC: Clarify docstring for `sigma` parameter for `curve_fit`
DOC: Clarify docstring for `sigma` parameter for `curve_fit`

Fixes #3682

jonycgn/scipy,dch312/scipy,woodscn/scipy,WarrenWeckesser/scipy,josephcslater/scipy,FRidh/scipy,felipebetancur/scipy,sonnyhu/scipy,sriki18/scipy,gertingold/scipy,vanpact/scipy,maciejkula/scipy,Eric89GXL/scipy,ndchorley/scipy,Shaswat27/scipy,Srisai85/scipy,piyush0609/scipy,chatcannon/scipy,rgommers/scipy,Eric89GXL/scipy,scipy/scipy,WarrenWeckesser/scipy,apbard/scipy,mgaitan/scipy,perimosocordiae/scipy,argriffing/scipy,aeklant/scipy,kleskjr/scipy,zxsted/scipy,jjhelmus/scipy,ales-erjavec/scipy,felipebetancur/scipy,jjhelmus/scipy,newemailjdm/scipy,gef756/scipy,jakevdp/scipy,njwilson23/scipy,arokem/scipy,gfyoung/scipy,pizzathief/scipy,felipebetancur/scipy,mortonjt/scipy,FRidh/scipy,efiring/scipy,jor-/scipy,witcxc/scipy,Kamp9/scipy,pnedunuri/scipy,ortylp/scipy,endolith/scipy,pschella/scipy,vhaasteren/scipy,Gillu13/scipy,mtrbean/scipy,jonycgn/scipy,trankmichael/scipy,surhudm/scipy,anielsen001/scipy,mtrbean/scipy,Stefan-Endres/scipy,dch312/scipy,mortada/scipy,woodscn/scipy,gdooper/scipy,Eric89GXL/scipy,larsmans/scipy,befelix/scipy,anntzer/scipy,nvoron23/scipy,niknow/scipy,futurulus/scipy,FRidh/scipy,gfyoung/scipy,vanpact/scipy,raoulbq/scipy,aarchiba/scipy,mgaitan/scipy,mortonjt/scipy,maniteja123/scipy,dominicelse/scipy,pschella/scipy,Srisai85/scipy,andyfaff/scipy,maciejkula/scipy,rgommers/scipy,aman-iitj/scipy,maniteja123/scipy,mortada/scipy,Dapid/scipy,cpaulik/scipy,andim/scipy,tylerjereddy/scipy,behzadnouri/scipy,zaxliu/scipy,pnedunuri/scipy,dch312/scipy,gfyoung/scipy,argriffing/scipy,ales-erjavec/scipy,jsilter/scipy,jsilter/scipy,giorgiop/scipy,behzadnouri/scipy,mgaitan/scipy,dch312/scipy,josephcslater/scipy,mortonjt/scipy,Gillu13/scipy,perimosocordiae/scipy,fredrikw/scipy,ilayn/scipy,FRidh/scipy,jsilter/scipy,jseabold/scipy,jakevdp/scipy,mortada/scipy,Dapid/scipy,jseabold/scipy,zerothi/scipy,anielsen001/scipy,mdhaber/scipy,FRidh/scipy,aeklant/scipy,rmcgibbo/scipy,petebachant/scipy,Newman101/scipy,jsilter/scipy,pbrod/scipy,lhilt/scipy,cpaulik/scipy,mortada/scipy,andyfaff/scipy,matthew-brett/scipy,mhogg/scipy,Kamp9/scipy,anntzer/scipy,rmcgibbo/scipy,mdhaber/scipy,zerothi/scipy,lukauskas/scipy,haudren/scipy,mortonjt/scipy,apbard/scipy,bkendzior/scipy,jakevdp/scipy,mortonjt/scipy,maniteja123/scipy,raoulbq/scipy,nmayorov/scipy,minhlongdo/scipy,kalvdans/scipy,vberaudi/scipy,ndchorley/scipy,andyfaff/scipy,Newman101/scipy,Stefan-Endres/scipy,matthew-brett/scipy,vigna/scipy,Newman101/scipy,Stefan-Endres/scipy,befelix/scipy,newemailjdm/scipy,rmcgibbo/scipy,fernand/scipy,vhaasteren/scipy,tylerjereddy/scipy,scipy/scipy,rgommers/scipy,niknow/scipy,andim/scipy,mortonjt/scipy,jonycgn/scipy,jseabold/scipy,larsmans/scipy,Newman101/scipy,mortada/scipy,lukauskas/scipy,rgommers/scipy,mdhaber/scipy,nonhermitian/scipy,e-q/scipy,ilayn/scipy,vanpact/scipy,ndchorley/scipy,ndchorley/scipy,kleskjr/scipy,mortada/scipy,Eric89GXL/scipy,zerothi/scipy,aeklant/scipy,minhlongdo/scipy,vberaudi/scipy,dominicelse/scipy,jonycgn/scipy,Stefan-Endres/scipy,vigna/scipy,jor-/scipy,maciejkula/scipy,anielsen001/scipy,pschella/scipy,anielsen001/scipy,behzadnouri/scipy,pizzathief/scipy,aman-iitj/scipy,person142/scipy,aarchiba/scipy,sonnyhu/scipy,chatcannon/scipy,vhaasteren/scipy,pnedunuri/scipy,jor-/scipy,pyramania/scipy,jseabold/scipy,dominicelse/scipy,ales-erjavec/scipy,petebachant/scipy,gdooper/scipy,Kamp9/scipy,nmayorov/scipy,mhogg/scipy,andim/scipy,WillieMaddox/scipy,befelix/scipy,person142/scipy,petebachant/scipy,aarchiba/scipy,niknow/scipy,ilayn/scipy,grlee77/scipy,vigna/scipy,person142/scipy,dominicelse/scipy,kleskjr/scipy,giorgiop/scipy,befelix/scipy,gertingold/scipy,newemailjdm/scipy,jamestwebber/scipy,Kamp9/scipy,trankmichael/scipy,endolith/scipy,surhudm/scipy,efiring/scipy,raoulbq/scipy,cpaulik/scipy,haudren/scipy,mhogg/scipy,gef756/scipy,niknow/scipy,pyramania/scipy,Shaswat27/scipy,matthewalbani/scipy,ChanderG/scipy,witcxc/scipy,sriki18/scipy,piyush0609/scipy,richardotis/scipy,Kamp9/scipy,futurulus/scipy,sauliusl/scipy,trankmichael/scipy,vigna/scipy,andim/scipy,njwilson23/scipy,perimosocordiae/scipy,tylerjereddy/scipy,larsmans/scipy,nvoron23/scipy,pyramania/scipy,andim/scipy,jakevdp/scipy,pbrod/scipy,argriffing/scipy,bkendzior/scipy,ales-erjavec/scipy,apbard/scipy,pschella/scipy,fredrikw/scipy,petebachant/scipy,WillieMaddox/scipy,vigna/scipy,aman-iitj/scipy,sauliusl/scipy,lhilt/scipy,zxsted/scipy,jamestwebber/scipy,gef756/scipy,anntzer/scipy,argriffing/scipy,piyush0609/scipy,woodscn/scipy,piyush0609/scipy,hainm/scipy,witcxc/scipy,maniteja123/scipy,aarchiba/scipy,hainm/scipy,fredrikw/scipy,matthewalbani/scipy,Shaswat27/scipy,kleskjr/scipy,pyramania/scipy,WillieMaddox/scipy,lukauskas/scipy,witcxc/scipy,piyush0609/scipy,ilayn/scipy,richardotis/scipy,mikebenfield/scipy,chatcannon/scipy,Srisai85/scipy,fernand/scipy,aman-iitj/scipy,niknow/scipy,grlee77/scipy,jamestwebber/scipy,kleskjr/scipy,gef756/scipy,kalvdans/scipy,mingwpy/scipy,mingwpy/scipy,larsmans/scipy,mgaitan/scipy,anntzer/scipy,newemailjdm/scipy,maciejkula/scipy,andyfaff/scipy,person142/scipy,pizzathief/scipy,fredrikw/scipy,mtrbean/scipy,sonnyhu/scipy,zaxliu/scipy,grlee77/scipy,nvoron23/scipy,ndchorley/scipy,minhlongdo/scipy,pyramania/scipy,Kamp9/scipy,befelix/scipy,sriki18/scipy,mdhaber/scipy,mgaitan/scipy,mikebenfield/scipy,josephcslater/scipy,niknow/scipy,nmayorov/scipy,e-q/scipy,endolith/scipy,WillieMaddox/scipy,rmcgibbo/scipy,ilayn/scipy,matthewalbani/scipy,zxsted/scipy,minhlongdo/scipy,bkendzior/scipy,maniteja123/scipy,gertingold/scipy,njwilson23/scipy,efiring/scipy,efiring/scipy,vanpact/scipy,haudren/scipy,Gillu13/scipy,e-q/scipy,sriki18/scipy,ortylp/scipy,haudren/scipy,Dapid/scipy,aeklant/scipy,scipy/scipy,jonycgn/scipy,zxsted/scipy,fernand/scipy,mikebenfield/scipy,sonnyhu/scipy,sauliusl/scipy,gdooper/scipy,WarrenWeckesser/scipy,mikebenfield/scipy,mdhaber/scipy,pnedunuri/scipy,mikebenfield/scipy,argriffing/scipy,pbrod/scipy,lukauskas/scipy,endolith/scipy,Gillu13/scipy,richardotis/scipy,ChanderG/scipy,witcxc/scipy,zaxliu/scipy,fernand/scipy,kalvdans/scipy,fredrikw/scipy,matthew-brett/scipy,mgaitan/scipy,vhaasteren/scipy,endolith/scipy,WarrenWeckesser/scipy,lukauskas/scipy,aarchiba/scipy,nonhermitian/scipy,richardotis/scipy,Gillu13/scipy,zerothi/scipy,zxsted/scipy,fernand/scipy,Stefan-Endres/scipy,tylerjereddy/scipy,matthewalbani/scipy,lhilt/scipy,arokem/scipy,gfyoung/scipy,maciejkula/scipy,Eric89GXL/scipy,vhaasteren/scipy,jseabold/scipy,hainm/scipy,zaxliu/scipy,person142/scipy,anielsen001/scipy,WarrenWeckesser/scipy,kalvdans/scipy,nmayorov/scipy,mhogg/scipy,njwilson23/scipy,Dapid/scipy,anielsen001/scipy,newemailjdm/scipy,mtrbean/scipy,minhlongdo/scipy,mdhaber/scipy,njwilson23/scipy,gertingold/scipy,cpaulik/scipy,jseabold/scipy,sauliusl/scipy,gdooper/scipy,surhudm/scipy,grlee77/scipy,gfyoung/scipy,apbard/scipy,aman-iitj/scipy,nonhermitian/scipy,gef756/scipy,nvoron23/scipy,petebachant/scipy,ortylp/scipy,mhogg/scipy,larsmans/scipy,Dapid/scipy,futurulus/scipy,Shaswat27/scipy,chatcannon/scipy,WillieMaddox/scipy,pbrod/scipy,behzadnouri/scipy,ilayn/scipy,zxsted/scipy,surhudm/scipy,mtrbean/scipy,felipebetancur/scipy,WillieMaddox/scipy,grlee77/scipy,mingwpy/scipy,jor-/scipy,jamestwebber/scipy,futurulus/scipy,vberaudi/scipy,woodscn/scipy,jsilter/scipy,e-q/scipy,andyfaff/scipy,scipy/scipy,giorgiop/scipy,fredrikw/scipy,sonnyhu/scipy,rgommers/scipy,Stefan-Endres/scipy,ortylp/scipy,ChanderG/scipy,richardotis/scipy,pschella/scipy,arokem/scipy,rmcgibbo/scipy,giorgiop/scipy,newemailjdm/scipy,nvoron23/scipy,hainm/scipy,jonycgn/scipy,ndchorley/scipy,Srisai85/scipy,ChanderG/scipy,fernand/scipy,andyfaff/scipy,vhaasteren/scipy,futurulus/scipy,Srisai85/scipy,giorgiop/scipy,e-q/scipy,WarrenWeckesser/scipy,andim/scipy,arokem/scipy,behzadnouri/scipy,nonhermitian/scipy,larsmans/scipy,hainm/scipy,lhilt/scipy,jjhelmus/scipy,vberaudi/scipy,trankmichael/scipy,efiring/scipy,anntzer/scipy,matthewalbani/scipy,zerothi/scipy,scipy/scipy,felipebetancur/scipy,nonhermitian/scipy,piyush0609/scipy,argriffing/scipy,petebachant/scipy,sriki18/scipy,trankmichael/scipy,raoulbq/scipy,aman-iitj/scipy,perimosocordiae/scipy,gertingold/scipy,ortylp/scipy,Srisai85/scipy,efiring/scipy,jamestwebber/scipy,mingwpy/scipy,zaxliu/scipy,dch312/scipy,njwilson23/scipy,Shaswat27/scipy,futurulus/scipy,mingwpy/scipy,endolith/scipy,hainm/scipy,sauliusl/scipy,kalvdans/scipy,trankmichael/scipy,Newman101/scipy,woodscn/scipy,anntzer/scipy,sonnyhu/scipy,Newman101/scipy,lhilt/scipy,surhudm/scipy,Gillu13/scipy,behzadnouri/scipy,vanpact/scipy,pizzathief/scipy,ortylp/scipy,chatcannon/scipy,nvoron23/scipy,cpaulik/scipy,minhlongdo/scipy,woodscn/scipy,josephcslater/scipy,pnedunuri/scipy,pizzathief/scipy,cpaulik/scipy,gdooper/scipy,nmayorov/scipy,giorgiop/scipy,bkendzior/scipy,FRidh/scipy,maniteja123/scipy,jor-/scipy,josephcslater/scipy,chatcannon/scipy,raoulbq/scipy,perimosocordiae/scipy,zerothi/scipy,dominicelse/scipy,bkendzior/scipy,vanpact/scipy,Shaswat27/scipy,apbard/scipy,jakevdp/scipy,ales-erjavec/scipy,jjhelmus/scipy,scipy/scipy,zaxliu/scipy,Dapid/scipy,haudren/scipy,felipebetancur/scipy,vberaudi/scipy,gef756/scipy,aeklant/scipy,pnedunuri/scipy,mingwpy/scipy,haudren/scipy,pbrod/scipy,raoulbq/scipy,Eric89GXL/scipy,mhogg/scipy,richardotis/scipy,kleskjr/scipy,sriki18/scipy,matthew-brett/scipy,ChanderG/scipy,rmcgibbo/scipy,ChanderG/scipy,vberaudi/scipy,perimosocordiae/scipy,arokem/scipy,pbrod/scipy,sauliusl/scipy,matthew-brett/scipy,ales-erjavec/scipy,tylerjereddy/scipy,lukauskas/scipy,surhudm/scipy,mtrbean/scipy,jjhelmus/scipy