Update readme

Author: rpidanny

README.md

@@ -11,8 +11,37 @@ AWS Lambda layer with ffmpeg binaries.
 - `opus`
 - `vpx`
 
+## Usage
+
+Click on Layers and choose `Add a layer`, and `Provide a layer version ARN` and enter the following ARN (replace eu-west-1 with the region of your Lambda):
+
+```
+arn:aws:lambda:eu-west-1:175033217214:layer:ffmpeg:1
+```
+
+![Provide layer ARN](img/usage.png "Provide layer ARN screenshot")
+
 ## Version ARNs
 
 | Ffmpeg version | ARN |
 | --- | --- |
 | 4.1.3 | `arn:aws:lambda:<region>:175033217214:layer:ffmpeg:1` |
+
+## Available Regions
+
+- `ap-northeast-1`
+- `ap-northeast-2`
+- `ap-south-1`
+- `ap-southeast-1`
+- `ap-southeast-2`
+- `ca-central-1`
+- `eu-north-1`
+- `eu-central-1`
+- `eu-west-1`
+- `eu-west-2`
+- `eu-west-3`
+- `sa-east-1`
+- `us-east-1`
+- `us-east-2`
+- `us-west-1`
+- `us-west-2`