add example for parameters usage in README.md
add example for parameters usage in README.md

I once created a [question and resolved it by myself for this PR](https://stackoverflow.com/q/51732908/5037430).

I thought it would be a nice idea to clarify the parameters usage with an example in the `README.md`.

Thanks for this awesome repo.
bryanburgers/node-mustache-express,bryanburgers/node-mustache-express,bryanburgers/node-mustache-express