Update AWS readme

Author: tidal

src/Aws/README.md

@@ -1 +1,23 @@
-Readme for opentelemetry-php-contrib AWS package (temporary file)
+
+## Installation
+
+### 1.1. Install PHP library/SDK dependencies
+
+Take a look at the documentation of the  [PHP library](https://github.com/open-telemetry/opentelemetry-php) on how to install its dependencies.
+
+### 1.2. Install the Package
+
+1. Add
+```bash
+    "minimum-stability": "dev",
+    "prefer-stable": true,
+```
+
+To your project's `composer.json` file, as this utility has not reached a stable release status yet.
+
+2. Install the package with composer:
+
+```bash
+$ composer require open-telemetry/contrib-aws
+```
+