add transformation documention

[Adtrex]

Resolves #5

The attach media function allows for two parameters attachmedia($file,$options). The transformation can be added to the $options variable. I have documented how to do that in the readme.

[unicodeveloper]

Thank you so much for your contribution. This is amazing! @Adtrex

[colbyfayock]

@Adtrex congrats on the merged PR! since it's officially October, you've always qualified for Hacktoberfest swag! please email hacktoberfest@cloudinary.com with your github username and a link to your contribution where I'll follow up to request more information for getting you your swag

https://cloudinary.com/blog/hacktoberfest-celebrate-open-source-sdks