Update contributing doc (#144)

Author: tianchu

CONTRIBUTING.md

@@ -2,19 +2,47 @@
 
 We love pull requests. Here's a quick guide.
 
-Fork, then clone:
-
-```bash
-git clone [email protected]:your-username/datadog-lambda-js.git
-```
-
-Make your change, update tests and ensure the tests pass (install Docker if you haven't):
-
-```bash
-npm test
-```
-
-Push to your fork and [submit a pull request][pr].
+1. Fork, clone and branch off `main`:
+    ```bash
+    git clone [email protected]:<your-username>/datadog-lambda-js.git
+    git checkout -b <my-branch>
+    ```
+1. Install the repositories dependencies, `yarn install`.
+1. Make your changes.
+1. Test your Lambda function against the locally modified version of Datadog Lambda library.
+   * The easiest approach is to use [yarn link](https://classic.yarnpkg.com/en/docs/cli/link/).
+
+     ```bash
+     yarn build # rebuild after changes
+     cd dist
+     yarn link
+     cd /path/to/your/testing/function/
+     yarn link "datadog-lambda-js" # use unlink after done
+     ```
+   * You can also build and publish a Lambda layer to your own AWS account and use it for testing.
+
+     ```bash
+     # Build layers using docker
+     ./scripts/build_layers.sh
+
+     # Publish the a testing layer to your own AWS account, and the ARN will be returned
+     # Example: ./scripts/publish_layers.sh us-east-1
+     ./scripts/publish_layers.sh <AWS_REGION>
+     ```
+ 
+1. Update tests and ensure they pass
+    ```bash
+    yarn test
+    ```
+1. Run the integration tests against your own AWS account and Datadog org (or ask a Datadog member to run):
+   ```bash
+   BUILD_LAYERS=true DD_API_KEY=<your Datadog api key> ./scripts/run_integration_tests.sh
+   ```
+1. Update integration test snapshots if needed:
+   ```bash
+   UPDATE_SNAPSHOTS=true DD_API_KEY=<your Datadog api key> ./scripts/run_integration_tests.sh
+   ```
+1. Push to your fork and [submit a pull request][pr].
 
 [pr]: https://github.com/your-username/datadog-lambda-js/compare/DataDog:main..main.
 

README.md

@@ -2,7 +2,7 @@
 ![build](https://github.com/DataDog/datadog-lambda-js/workflows/build/badge.svg)
 [![Code Coverage](https://img.shields.io/codecov/c/github/DataDog/datadog-lambda-js)](https://codecov.io/gh/DataDog/datadog-lambda-js)
 [![NPM](https://img.shields.io/npm/v/datadog-lambda-js)](https://www.npmjs.com/package/datadog-lambda-js)
-[![Slack](https://img.shields.io/badge/slack-%23serverless-blueviolet?logo=slack)](https://datadoghq.slack.com/channels/serverless/)
+[![Slack](https://chat.datadoghq.com/badge.svg?bg=632CA6)](https://chat.datadoghq.com/)
 [![License](https://img.shields.io/badge/license-Apache--2.0-blue)](https://github.com/DataDog/datadog-lambda-js/blob/main/LICENSE)
 
 Datadog Lambda Library for Node.js enables enhanced Lambda metrics, distributed tracing, and custom metric submission from AWS Lambda functions.
@@ -117,6 +117,10 @@ You can also open an issue for a feature request.
 
 If you find an issue with this package and have a fix, please feel free to open a pull request following the [procedures](https://github.com/DataDog/dd-lambda-js/blob/main/CONTRIBUTING.md).
 
+## Community
+
+For product feedback and questions, join the `#serverless` channel in the [Datadog community on Slack](https://chat.datadoghq.com/).
+
 ## License
 
 Unless explicitly stated otherwise all files in this repository are licensed under the Apache License Version 2.0.