docs(README): smoke test / Probot v11 migration key points / common errors (#63)

Author: axel3rd

.gitignore

@@ -1 +1,3 @@
 node_modules/
+.settings/
+.project

README.md

@@ -49,12 +49,45 @@ functions:
 
 Make sure to configure your GitHub App registration's webhook URL to `<your lambda's URL>/api/github/webhooks`.
 
+## Test deployment
+
+For testing your Probot deployment without end to end (GitHub) integration, you can use this shell snippet:
+
+```shell
+$ LAMBDA_URL=https://x.execute-api.y.amazonaws.com/stage-or-basePath/api/github/webhooks
+$ SECRET=the_webhook_secret
+$ TMP_DATA_FILE=/tmp/smoke.data
+
+$ echo -n "{\"action\":\"test\"}" > $TMP_DATA_FILE
+$ SIGN=$(openssl dgst -sha1 -hmac $SECRET $TMP_DATA_FILE | cut -d" " -f2)
+$ curl --request POST --header "X-Hub-Signature: sha1=$SIGN" --header "X-Github-Event: test" --header "X-GitHub-Delivery: fake" --data-binary "@$TMP_DATA_FILE" $LAMBDA_URL
+{"ok":true}        <-- Concent for Probot v10: {"message":"Received test.test"}
+```
+
 ## Examples
 
 - [example-aws-lambda-serverless](https://github.com/probot/example-aws-lambda-serverless/#readme) - Official example application that is continuously deployed to AWS Lambda
 
 Add yours!
 
+## Common errors
+
+| Http Code | Message                      | Description                                                                                        |
+| --------- | ---------------------------- | -------------------------------------------------------------------------------------------------- |
+| 403       | Missing Authentication Token | Bad endpoint (this one is not binded on Lambda)                                                    |
+| 500       | Internal server error        | Incorrect headers value (`X-GitHub-Delivery`, `X-GitHub-Event`, `X-Hub-Signature`) or Probot error |
+
+## Probot v11 migration key points
+
+For Probot v11 support, this adapter introduces significant changes. Here the key points to update (in addition of [Probot v11 breaking changes](https://github.com/probot/probot/releases/tag/v11.0.0)):
+
+| Key point / Probot   | <= v10                                                                                      | >= v11                                  |
+| -------------------- | ------------------------------------------------------------------------------------------- | --------------------------------------- |
+| NPM package name     | `@probot/serverless-lambda`                                                                 | `@probot/adapter-aws-lambda-serverless` |
+| _handler.js_ content | See [Usage v1.x](https://github.com/probot/adapter-aws-lambda-serverless/tree/v1.0.2#usage) | See [Usage](#usage)                     |
+| AWS Lambda Runtime   | `handler.probot`                                                                            | `handler.webhooks`                      |
+| AWS Lambda Handler   | Node.js 12.x _(preferred)_                                                                  | Node.js 12.x _(required)_               |
+
 ## LICENSE
 
 [ISC](LICENSE)