Document necessary preferences for running on HarmonyOS NEXT

[jschwe]

On HarmonyOS NEXT JIT is forbidden by the system policy, so one needs to disable JIT in the servo preferences.
In the future we could perhaps during startup check in servo / the embedder if JIT is possible and disable JIT based on the result of those checks, but for now it is sufficient to document the required preferences.

prefs.json:

  "js.disable_jit": true,

[sagudev]

Isn't js.disable_jit enough? I think it disables JIT globally so other options should be nop.

[jschwe]

Thanks! Indeed just js.disable_jit is enough. I'm not sure why it didn't work the first time I tried - maybe I forgot to rebuild or something...