Add docs on JS API support

docs/docs-using-js-api-support.md

@@ -0,0 +1,32 @@
+# JavaScript API Support
+
+Javy by default supports all the JavaScript features and APIs provided by
+QuickJS, plus partial support for additional APIs. 
+
+This document aims to give an overview of the additional APIs provided by Javy.
+
+In general the ultimate goal of Javy is to provide a [WinterCG  Common
+API](https://common-min-api.proposal.wintercg.org/#api-index) compatible
+implementation, however, currently some APIs are not fully
+compliant and therefore are provided under a custom `Javy` namespace or
+explicitly marked as partially supported in the table below.
+
+## Compatibility table
+
+|API|Support|Comments|
+|:-:|:-:|:-:|
+|`JSON`|✅| Improved performace through SIMD JSON, when using the `-J simd-json-builtins` flag|
+|`TexDecoder`|🚧| Partial support, not fully compliant|
+|`TextEncoder`|🚧| Partial support, not fully compliant|
+|`TextEncoder`|🚧| Partial support, not fully compliant|
+|`console`|🚧| Partial support, `console.log` and `console.error`|
+
+Javy provides a custom `Javy` naespace, which includes the following
+functionality:
+
+* `IO`: provides `readSync` and `writeSync`, analogous to [Node's `fs`
+  API](https://nodejs.org/api/fs.html).
+
+* `JSON`: provides `fromStdin()` and `toStdout()`. Which are helpers to read or
+  write from and to a file descriptor when working with `JSON`.
+

docs/index.md

@@ -6,6 +6,7 @@
 * [Extending](./docs-using-extending.md)
 * [Exporting functions](./docs-using-exports.md)
 * [Invoking modules](./docs-using-invoking.md)
+* [JavaScript API Support](./docs-using-js-api-support.md)
 
 ## Contributing