Clarify a section in the expand() docstring
Clarify a section in the expand() docstring

kevalds51/sympy,cswiercz/sympy,ChristinaZografou/sympy,Mitchkoens/sympy,dqnykamp/sympy,mcdaniel67/sympy,bukzor/sympy,lindsayad/sympy,pbrady/sympy,flacjacket/sympy,yashsharan/sympy,AunShiLord/sympy,ChristinaZografou/sympy,kmacinnis/sympy,maniteja123/sympy,diofant/diofant,skidzo/sympy,shikil/sympy,postvakje/sympy,Davidjohnwilson/sympy,jbbskinny/sympy,kmacinnis/sympy,maniteja123/sympy,hargup/sympy,chaffra/sympy,saurabhjn76/sympy,abhiii5459/sympy,sahilshekhawat/sympy,srjoglekar246/sympy,yukoba/sympy,abhiii5459/sympy,Vishluck/sympy,madan96/sympy,lidavidm/sympy,Gadal/sympy,mcdaniel67/sympy,lindsayad/sympy,wanglongqi/sympy,sahmed95/sympy,wyom/sympy,sahmed95/sympy,cccfran/sympy,Mitchkoens/sympy,grevutiu-gabriel/sympy,yashsharan/sympy,rahuldan/sympy,aktech/sympy,Shaswat27/sympy,abloomston/sympy,asm666/sympy,amitjamadagni/sympy,jaimahajan1997/sympy,Vishluck/sympy,sunny94/temp,grevutiu-gabriel/sympy,dqnykamp/sympy,amitjamadagni/sympy,toolforger/sympy,sahilshekhawat/sympy,hrashk/sympy,Designist/sympy,cccfran/sympy,pandeyadarsh/sympy,ChristinaZografou/sympy,ahhda/sympy,kaushik94/sympy,moble/sympy,liangjiaxing/sympy,Arafatk/sympy,Davidjohnwilson/sympy,Designist/sympy,drufat/sympy,mafiya69/sympy,skidzo/sympy,wanglongqi/sympy,farhaanbukhsh/sympy,debugger22/sympy,garvitr/sympy,jaimahajan1997/sympy,liangjiaxing/sympy,chaffra/sympy,AunShiLord/sympy,iamutkarshtiwari/sympy,drufat/sympy,yukoba/sympy,Shaswat27/sympy,kevalds51/sympy,jamesblunt/sympy,Designist/sympy,abloomston/sympy,sampadsaha5/sympy,rahuldan/sympy,abhiii5459/sympy,atreyv/sympy,lidavidm/sympy,wyom/sympy,asm666/sympy,jamesblunt/sympy,dqnykamp/sympy,madan96/sympy,lidavidm/sympy,hrashk/sympy,oliverlee/sympy,Curious72/sympy,MridulS/sympy,kumarkrishna/sympy,kaichogami/sympy,wyom/sympy,beni55/sympy,pbrady/sympy,ga7g08/sympy,garvitr/sympy,Gadal/sympy,skidzo/sympy,mafiya69/sympy,Sumith1896/sympy,souravsingh/sympy,toolforger/sympy,lindsayad/sympy,jerli/sympy,pandeyadarsh/sympy,rahuldan/sympy,debugger22/sympy,shipci/sympy,iamutkarshtiwari/sympy,asm666/sympy,sampadsaha5/sympy,ahhda/sympy,toolforger/sympy,yukoba/sympy,bukzor/sympy,iamutkarshtiwari/sympy,AkademieOlympia/sympy,postvakje/sympy,emon10005/sympy,ga7g08/sympy,sunny94/temp,moble/sympy,cswiercz/sympy,jbbskinny/sympy,Vishluck/sympy,atsao72/sympy,aktech/sympy,wanglongqi/sympy,sahilshekhawat/sympy,yashsharan/sympy,Titan-C/sympy,skirpichev/omg,ga7g08/sympy,atreyv/sympy,postvakje/sympy,AkademieOlympia/sympy,atreyv/sympy,AunShiLord/sympy,debugger22/sympy,aktech/sympy,souravsingh/sympy,bukzor/sympy,Shaswat27/sympy,meghana1995/sympy,Davidjohnwilson/sympy,sahmed95/sympy,maniteja123/sympy,meghana1995/sympy,MechCoder/sympy,Curious72/sympy,emon10005/sympy,shikil/sympy,liangjiaxing/sympy,garvitr/sympy,cccfran/sympy,Arafatk/sympy,beni55/sympy,moble/sympy,vipulroxx/sympy,VaibhavAgarwalVA/sympy,MechCoder/sympy,emon10005/sympy,saurabhjn76/sympy,farhaanbukhsh/sympy,hargup/sympy,atsao72/sympy,pbrady/sympy,hrashk/sympy,Mitchkoens/sympy,chaffra/sympy,jerli/sympy,Sumith1896/sympy,kevalds51/sympy,Sumith1896/sympy,Titan-C/sympy,farhaanbukhsh/sympy,grevutiu-gabriel/sympy,kaichogami/sympy,kmacinnis/sympy,drufat/sympy,MridulS/sympy,abloomston/sympy,jbbskinny/sympy,AkademieOlympia/sympy,kaichogami/sympy,kumarkrishna/sympy,MechCoder/sympy,Gadal/sympy,mafiya69/sympy,kaushik94/sympy,jaimahajan1997/sympy,VaibhavAgarwalVA/sympy,meghana1995/sympy,hargup/sympy,jerli/sympy,pandeyadarsh/sympy,VaibhavAgarwalVA/sympy,vipulroxx/sympy,Arafatk/sympy,ahhda/sympy,kumarkrishna/sympy,cswiercz/sympy,saurabhjn76/sympy,kaushik94/sympy,Curious72/sympy,souravsingh/sympy,Titan-C/sympy,madan96/sympy,shipci/sympy,shipci/sympy,mcdaniel67/sympy,beni55/sympy,atsao72/sympy,jamesblunt/sympy,MridulS/sympy,sampadsaha5/sympy,vipulroxx/sympy,shikil/sympy,sunny94/temp,oliverlee/sympy,oliverlee/sympy