Add a Download page

[nbp]

Some people are able to find jsc and v8, but report that there is no JS runtime based on SpiderMonkey.

By adding download page, where we can list mozjs library, and how it is packaged, and how to install it on various system or as a dependency for embedding might help get traction and better reports from users.

[hotsphink]

+1

Though I'll note that in the specific case you link, I attempted to run the benchmark using the spidermonkey shell. First, it required fiddling with the module search path and running with the -m flag, which is fine. But it couldn't load modules from node_modules/, seemingly because they were compiled with something that structured in them in a way that worked with node and bun and various other things, but not our shell. The obvious reason was the mapping from module names to filesystem paths, but it wasn't just that -- the code that was executed did autodetection of various environments and skipped what was needed to set things up properly. Specifically in this case, there was a Benchmark object that should have a Benchmark.Suite property, but it feature-detected itself into a path that skipped the property set.

Anyway, my point is that while making it easier to download something and get a runnable shell is very important, we're still quite a ways from people being able to run nontrivial stuff (eg that uses existing module code) similarly to node or bun. We'd need the build tools to produce something compatible with our shell and module loader, for example.

I'm not sure why I'm saying this here. You already know this, and the download page is a good idea independently.