Add, improve docstrings for methods in fp_groups.py
Add, improve docstrings for methods in fp_groups.py

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