Instead of requiring an example host, use `wasmtime run --invoke`

[pchickey]

Having an example host is useful for showing how a host can work. When showing how guests can export an add interface, though, you can run them with wasmtime run --invoke "add(1,2)" ..., making a custom host one less concept that the user has to think about.

https://github.com/bytecodealliance/component-docs/blob/main/component-model/src/language-support/javascript.md#running-the-component-in-the-example-host

[vados-cosmonic]

Yep this would definitely further simplify the adder example -- it probably also makes sense to add a section about building hosts/building a custom host, and that's where the guide that uses that stuff could live. We could link to that section from the initial adder tutorial for those who want to go deeper.