Webassembly feature matrix

[bstrie]

The readme should contain a feature matrix giving an overview of webassembly support for each language. A very basic matrix can currently be found at, but we should flesh it out with information like wasi support, I/O support, socket support, etc.

[nickvidal]

Adding link to current matrix at Enarx Docs:

https://enarx.dev/docs/webassembly/introduction

And related issue:

enarx/website#36

[bstrie]

Not as useful for our purposes, but might be something worth linking to anyway: https://webassembly.org/roadmap/

[bstrie]

Would be useful to also document which languages we are currently automatically building as part of CI in this repo, as a marker of the maturity of each toolchain. Once we have all languages building we can then try making this repo the canonical location of the wasm docs that are currently living at enarx.dev, with the doc pages being automatically tested.