docs(lambda-at-edge): add initial documentation

Author: danielcondemarin

packages/lambda-at-edge/README.md

@@ -1,3 +1,51 @@
-### AWS Lambda@Edge toolbox to help you deploy serverless next.js applications to CloudFront
+### AWS Lambda@Edge library to help you deploy serverless next.js applications to CloudFront
 
-TODO: Contents
+This library was created to decouple the core logic of creating serverless rendered next.js applications on the Cloud agnostic of a specific provider. In other words, this library could be used to deploy via serverles components, AWS CDK, or any other providers you'd like.
+
+## Usage
+
+```
+const path = require('path');
+const { Builder } = require("@sls-next/lambda-at-edge");
+
+const nextConfigDir = '/dir/to/my/nextapp';
+const outputDir = path.join(nextConfigDir, ".serverless_nextjs"),
+
+const builder = new Builder(
+  nextConfigDir,
+  outputDir,
+  {
+    cmd: './node_modules/.bin/next',
+    cwd: process.cwd(),
+    env: {},
+    args: ['build']
+  }
+);
+
+await builder.build();
+```
+
+After running the above, the output directory will contain the Lambda@Edge handlers necessary to server side render at the edge.
+
+```
+/dir/to/my/next-app/.serverless_nextjs/
+
+ > default-lambda
+   > manifest.json
+   > pages/
+   > node_modules/next-aws-cloudfront/index.js
+   > index.js # handler
+
+ > api-lambda
+   > manifest.json
+   > pages/api/
+   > node_modules/next-aws-cloudfront/index.js
+   > index.js # handler
+```
+
+The handlers need to be attached to the `origin-request` trigger of CloudFront. The `api-lambda` edge function should be attached to a CloudFront behaviour that only triggers in the event of `/api/*` requests.
+
+### TODO:
+
+- Provisioning and configuration of the CloudFront distribution
+- Create a separate utility to clean up unused Lambda@Edge functions that were previously attached to a CloudFront distribution