Threads are enabled by default, contradicting the documentation

[TethysSvensson]

Describe the bug

The documentation on Features for v3.1.1 says that threads are disabled by default, however that is not the case.

Steps to reproduce

The following code crashes:

assert_eq!(wasmer::Features::new().threads, false);

Expected behavior

That the documentation matches the behavior.

[syrusakbary]

Good call. We need to fix this on the docs

[ptitSeb]

Need to check also the CLI to be able to disable threads.

[syrusakbary]

@ptitSeb we should enable them by default now (replicating browsers behavior), so we just need to update the docs

[ptitSeb]

Done with #3665