Documenting Solveset: The new 'Solver'

[AMiT Kumar]

As lot of people are not aware of the purpose of solveset , to answer questions

like why we are doing, what we are doing, We decided to open a PR , to document it. 

Where the community can participate and give their views and suggestions.

If there is anything you would like us to answer about solveset, please add a comment on:

https://github.com/sympy/sympy/pull/9500

Thanks,

AMiT Kumar