Expand the docstring of DotProduct, and add doctests
Expand the docstring of DotProduct, and add doctests

rahuldan/sympy,kaushik94/sympy,yashsharan/sympy,yashsharan/sympy,skidzo/sympy,skidzo/sympy,chaffra/sympy,chaffra/sympy,jaimahajan1997/sympy,chaffra/sympy,jaimahajan1997/sympy,aktech/sympy,drufat/sympy,drufat/sympy,kaushik94/sympy,postvakje/sympy,yashsharan/sympy,sampadsaha5/sympy,drufat/sympy,souravsingh/sympy,madan96/sympy,postvakje/sympy,madan96/sympy,souravsingh/sympy,jaimahajan1997/sympy,kaushik94/sympy,aktech/sympy,rahuldan/sympy,postvakje/sympy,sampadsaha5/sympy,aktech/sympy,madan96/sympy,souravsingh/sympy,skidzo/sympy,rahuldan/sympy,sampadsaha5/sympy