Update README.md

Author: henhal

README.md

@@ -1,2 +1,58 @@
 # serverless-plugin-layer-manager
-Plugin for the Serverless framework that offers improved AWS Lambda layer management
+Plugin for the Serverless framework that offers improved AWS Lambda layer management.
+
+The Serverless framework supports AWS Lambda layers, but there are some shortcomings:
+
+* When creating Node.JS layers from local directories you create a directory containing a `nodejs` folder with a `package.json` file in it. However, the Serverless framework will not automatically install the dependencies used by the layer, so it needs to be done manually using e.g. hooks.
+
+* Layers are not exported by default. To export a layer you must declare your XxxLambdaLayer resources under `Output` and add an `Export` property manually
+
+* If using `retain: true` on your layers, it's not possible to reference them from functions in the same stack, since layer names will be appended with a unique version hash. You either need to stop using `retain` or put your layers in a separate stack and export them using the trick above, and then reference them from your functions in another stack.
+
+This plugin fixes all these problems by automatically adding hooks to invoke `npm install` on each declared Node.JS layer, and by transforming the generated CloudFormation template to export the layers and to properly reference the versioned layers from functions.
+
+Installation:
+
+```
+npm install --save-dev serverless-plugin-layer-manager
+```
+
+serverless.yml:
+
+```
+...
+plugins:
+  - serverless-plugin-layer-manager
+```
+
+That's it! You may now reference your layers from functions in the same file like
+
+```
+layers:
+  lib:
+    path: lib
+    name: dev-foo-lib
+    description: My library
+    retain: true
+    
+functions:
+  hello:
+    handler: index.handler
+    layers:
+      - !Ref: LibLambdaLayer # TitleCase layer name followed by LambdaLayer 
+```
+
+The `lib` layer will be installed and its `node_modules` packaged into the artifact, and the function will use the layer.
+
+You may customize the features by adding a `layerConfig` object under `custom`, supporting the following properties:
+
+```
+custom:
+  layerConfig:
+    installLayers: <boolean>
+    exportLayers: <boolean>
+    upgradeLayerReferences: <boolean>
+    exportPrefix: <prefix used for the names of the exported layers>
+```
+
+By default, all config options are true and the `exportPrefix` is set to `${AWS:StackName}-`.