Bring back the README for @glimmer/component (#20946)

Author: NullVoxPopuli

packages/@glimmer/component/README.md

@@ -0,0 +1,38 @@
+# @glimmer/component
+
+[![npm version](https://badge.fury.io/js/%40glimmer%2Fcomponent.svg)](https://badge.fury.io/js/%40glimmer%2Fcomponent)
+[![CI](https://github.com/emberjs/ember.js/workflows/CI/badge.svg)](https://github.com/emberjs/ember.js/actions?query=workflow%3ACI)
+
+## Installation
+
+Add this package to your project:
+
+```bash
+npm install --save-dev @glimmer/component
+```
+
+## Usage
+
+To use this in a Glimmer application, import the package and export an extended class:
+
+```glimmer-ts
+import Component from '@glimmer/component';
+
+export default class MyComponent extends Component {
+  get doubled() {
+    return this.args.foo * 2;
+  }
+
+  <template>
+    {{@foo}} * 2 === {{this.doubled}}
+  </template>
+}
+```
+
+## Contributing
+
+Bug reports and pull requests are welcome on GitHub at https://github.com/emberjs/ember.js
+
+## License
+
+MIT License.