example-dapp: Write a tutorial using this repo

[paulbellamy]

Write up a tutorial using this repo.

Tutorial should include:

• Clone the repo
• Set up and run it locally
• Tweak the contract
• Tweak the app
• Deploy id

[leighmcculloch]

If this tutorial is to capture this example, I'd add an example page instead of a tutorial page. I think when we discussed this previously I might have said tutorial but I meant example. The example pages are here: https://soroban.stellar.org/docs/category/examples

And then for a tutorial having a tutorial that demonstrates how to run the rpc server, and a super super basic use of the frontend SDK to invoke the contract. To go with the other tutorials here: https://soroban.stellar.org/docs/category/tutorials