docs(bidirectionality): bidirectionality how-to explanation

Author: EladBezalel

guides/bidirectionality.md

@@ -0,0 +1,22 @@
+# Angular Material bi-directionality
+
+### How to set your application direction
+The simplest way is applying `dir` attribute on either the `html` or `body` tags.
+All material components would automatically inherit the application direction.
+
+You can change the direction for a specific part of you application by applying `dir` attribute on the container element.
+
+### How to develop bi-directional components
+In your component import `Directionality` out of `@angular/cdk`
+And inject it in your component constructor
+```ts
+constructor(_dir: Directionality) {
+  console.log(_dir.value);
+}
+```
+Now you have access to the application direction,
+You can also subscribe to `change`:
+```ts
+_dir.change.subscribe(() => // DO SOMETHING );
+```
+And be notified for every direction change.