add a short explaining about plugins usages

test_plugin/README.md

@@ -0,0 +1,130 @@
+# Plugins
+
+Short explanation showing how Deno Rust plugins can be used. _**!!! warning the
+feature is still unstable!!!**_
+
+Clone the [deno](https://github.com/denoland/deno.git) source & go to
+`deno/test_plugin`
+
+The repo is structure as following:
+
+```
+test_plugin
+├── Cargo.toml
+├── src
+│   └── lib.rs
+└── tests
+    ├── ...
+    └── test.js
+```
+
+It is a rust repo.
+
+## In the `rust`
+
+#### 1- add `deno_core` & specify your project as a crate of type `cdylib` to make the lib dynamically available.
+
+In the cargo manifest
+
+```
+[package]
+name = "test_plugin"
+...
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+...
+
+deno_core = { path = "../core" }
+...
+```
+
+#### 2- wrap your custom lib functionalities in ops functions,
+
+```rust
+// in lib.rs
+fn op_test_sync(
+  _interface: &mut dyn Interface,
+  zero_copy: &mut [ZeroCopyBuf],
+) -> Op {
+
+  ...
+
+  Op::Sync(result_box)
+}
+```
+
+#### 3- register then inside the plugin container `deno_plugin_init`.
+
+```rust
+// in lib.rs
+#[no_mangle]
+pub fn deno_plugin_init(interface: &mut dyn Interface) {
+  interface.register_op("testSync", op_test_sync);
+  ...
+}
+```
+
+#### 4- build your lib with cargo : `cargo build -p <name of the crate>`
+
+```shell
+$ cargo build -p test_plugin --release
+```
+
+## In js
+
+#### 5- open your lib with `Deno.openPlugin`. You had to specify the build target from (4)
+
+```js
+// in test.js
+ const rid = Deno.openPlugin(<path to *.dylib>);
+```
+
+#### 6 - get your functionality from ops with `Deno.core.ops`
+
+```js
+// in test.js
+const { testSync } = Deno.core.ops();
+```
+
+#### 7 - dispatch call to your functionality with ops using `Deno.core.dispatch`
+
+```js
+// in test.js
+const response = Deno.core.dispatch(
+  testSync,
+  new Uint8Array([116, 101, 115, 116]),
+  new Uint8Array([49, 50, 51]),
+  new Uint8Array([99, 98, 97]),
+);
+```
+
+async ops:
+
+```js
+// in test.js
+Deno.core.setAsyncHandler(testAsync, (response) => {
+  console.log(`Plugin Async Response: ${textDecoder.decode(response)}`);
+});
+
+const response = Deno.core.dispatch(
+  testAsync,
+  new Uint8Array([116, 101, 115, 116]),
+  new Uint8Array([49, 50, 51]),
+);
+```
+
+#### 8 - close the plugin
+
+```
+// in test.js
+  Deno.close(rid);
+```
+
+#### 9 - run your script
+
+```shell
+$ deno run --allow-plugin --unstable tests/test.js release
+```