List alternative packages in the documentation

[rodrigoaguilera]

Summary

I was very happy to find this library on packagist to develop a salesforce integration but before that I stumbled upon
https://github.com/Kephson/php-salesforce-rest-api
that is not a a DBAL

Trineforce fits more my project needs and I don't have to worry about sanitizing the parameters for the queries since that is done by doctrine.

I also discovered an eloquent model for salesforce
https://github.com/roblesterjr04/EloquentSalesForce
but I don't want to use laravel for this particular project.

Describe the solution you'd like

My main goal is to make people aware of the alternatives so even if only the maintainer reads this issue is fine but I think it can be beneficial to have a little section in the readme that lists alternatives. I will propose the same on the other packages.