Renovate the WASI example

[ifsheldon]

Feature

Please renovate the WASI example in the documentation and the code, as they are using old wasi_common and super outdated wasmtime_wasi .

Benefit

Updating the doc and example should allow newcomers find latest stable way to run WASI components, instead of prehistoric workarounds.

Implementation

I can make a PR.

[fitzgen]

I can make a PR.

This would be wonderful, thanks!