add plugin example

Author: fpliger

docs/user-guide/plugins.md

@@ -12,5 +12,42 @@ core itself.
 Here's an example of how a PyScript plugin looks like:
 
 ```js
+// import the hooks from PyScript first...
+import { hooks } from "<path_to_pyscript>/core.js";
 
+// Use the `main` attribute on hooks do define plugins that run on the main thread
+hooks.main.onReady.add((wrap, element) => {
+    console.log("main", "onReady");
+    if (location.search === '?debug') {
+    console.debug("main", "wrap", wrap);
+    console.debug("main", "element", element);
+    }
+});
+hooks.main.onBeforeRun.add(() => {
+    console.log("main", "onBeforeRun");
+});
+hooks.main.codeBeforeRun.add('print("main", "codeBeforeRun")');
+hooks.main.codeAfterRun.add('print("main", "codeAfterRun")');
+hooks.main.onAfterRun.add(() => {
+    console.log("main", "onAfterRun");
+});
+
+// Use the `worker` attribute on hooks do define plugins that run on workers
+hooks.worker.onReady.add((wrap, xworker) => {
+    console.log("worker", "onReady");
+    if (location.search === '?debug') {
+    console.debug("worker", "wrap", wrap);
+    console.debug("worker", "xworker", xworker);
+    }
+});
+
+hooks.worker.onBeforeRun.add(() => {
+    console.log("worker", "onBeforeRun");
+});
+
+hooks.worker.codeBeforeRun.add('print("worker", "codeBeforeRun")');
+hooks.worker.codeAfterRun.add('print("worker", "codeAfterRun")');
+hooks.worker.onAfterRun.add(() => {
+    console.log("worker", "onAfterRun");
+});
 ```