Update index.js

[leeli0]

Add remarks for wildcard parameters of Express 5.x

[IamLizu]

Hi @UlisesGascon 👋

Did we have a plan to separate the examples from this repository?

[wesleytodd]

Yes I believe that is the plan: #5309

For now though, I am not a big fan of a version specific comment like this. The master branch now is v5, so if you are interested in examples for express@4 then I would suggest we direct folks to the 4.x branch.

EDIT: oops, early send.

That said, the other part of this change is good imo.

[leeli0]

Directly runing the example in the repository environment is perfect. Nevertheless, if try the example in a project and the npm install express@4 as default would cause some inconvenience. Also, Route parameters of Express 5.x API doesn't metion the use of wildcard parameters, so for newbies like me might feel confusing of the '/files/*file' route path.