Added more intro content in the mechanics docs.
Added more intro content in the mechanics docs.

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