improve readability of tip in motivation and samples section of generics.md

[hamirmahal]

I think we can improve the readability of the tip directly above the "Design Pattern: Convenience generic" section of the "Generics" page.

I created pull request #632 to close this.

Original paragraph: "TIP: You can call the generic parameter whatever you want. It is conventional to use T, U, V when you have simple generics. If you have more than one generic argument try to use meaningful names e.g. TKey and TValue (conventional to prefix with T as generics are also called templates in other languages e.g. C++)."

Paragraph if we merge #632: "TIP: You can call the generic parameter whatever you want. It is conventional to use T, U, or V when you have simple generics. If you have more than one generic argument, try to use meaningful names, like TKey and TValue. The convention is to prefix with T because generics are also called templates in other languages like C++."