Add Seenode deployment instructions to documentation

[GeoSegun]

Hey. Just wanted to add seenode to the listed providers, as we have first class support for flask. Thanks!

[davidism]

Thanks, it's always great to see services supporting Flask.

However, at this time we don't plan on adding more services to this list, as it is difficult to keep updated and fair. You'll notice that around that list, the docs say:

The links below are for some of the most common platforms

This list is not exhaustive, and you should evaluate these and other services based on your application’s needs.

I'll keep this in mind if I do change my mind.