Update README for ENTRYPOINT (#41)

Author: mullermp

README.md

@@ -1,16 +1,16 @@
 ## AWS Lambda Ruby Runtime Interface Client
 
-We have open-sourced a set of software packages, Runtime Interface Clients (RIC), that implement the Lambda
- [Runtime API](https://docs.aws.amazon.com/lambda/latest/dg/runtimes-api.html), allowing you to seamlessly extend your preferred
-  base images to be Lambda compatible.
-The Lambda Runtime Interface Client is a lightweight interface that allows your runtime to receive requests from and send requests to the Lambda service.
+We have open-sourced a set of software packages, Runtime Interface Clients (RIC), that implements the Lambda
+[Runtime API](https://docs.aws.amazon.com/lambda/latest/dg/runtimes-api.html), allowing you to seamlessly extend
+your preferred base images to be Lambda compatible.
+The Lambda Runtime Interface Client is a lightweight interface that allows your runtime to
+receive requests from and send requests to the Lambda service.
 
 The Lambda Ruby Runtime Interface Client is vended through [rubygems](https://rubygems.org/gems/aws_lambda_ric). 
 You can include this package in your preferred base image to make that base image Lambda compatible.
 
 ## Requirements
-The Ruby Runtime Interface Client package currently supports Ruby versions:
- - 3.2 and 3.3
+The Ruby Runtime Interface Client package currently supports ruby 3.0 and above.
 
 ## Usage
 
@@ -37,17 +37,9 @@ Or install it manually as:
 
     $ gem install aws_lambda_ric
 
-
-Next step would be to copy your Lambda function code into the image's working directory.
-```dockerfile
-# Copy function code
-RUN mkdir -p ${FUNCTION_DIR}
-COPY app.rb ${FUNCTION_DIR}
-
-WORKDIR ${FUNCTION_DIR}
-```
-
-The next step would be to set the `ENTRYPOINT` property of the Docker image to invoke the Runtime Interface Client and then set the `CMD` argument to specify the desired handler.
+The next step would be to copy your Lambda function code into the image's working directory.
+You will need to set the `ENTRYPOINT` property of the Docker image to invoke the Runtime Interface Client and
+then set the `CMD` argument to specify the desired handler.
 
 Example Dockerfile:
 ```dockerfile
@@ -84,7 +76,18 @@ ENTRYPOINT ["/usr/local/bin/aws_lambda_ric"]
 CMD ["app.App::Handler.process"]
 ```
 
-Example Ruby handler `app.rb`:
+Note that the `ENTRYPOINT` may differ based on the base image used. You can find the correct path by running an
+interactive shell in the container and checking the installed location of the gem.
+
+```shell script
+docker run -it --rm amazonlinux:latest bash
+yum install -y which ruby
+gem install aws_lambda_ric
+which aws_lambda_ric
+```
+
+Finally, create a Ruby handler. This is an example `app.rb`:
+
 ```ruby
 module App
   class Handler
@@ -97,7 +100,10 @@ end
 
 ### Local Testing
 
-To make it easy to locally test Lambda functions packaged as container images we open-sourced a lightweight web-server, Lambda Runtime Interface Emulator (RIE), which allows your function packaged as a container image to accept HTTP requests. You can install the [AWS Lambda Runtime Interface Emulator](https://github.com/aws/aws-lambda-runtime-interface-emulator) on your local machine to test your function. Then when you run the image function, you set the entrypoint to be the emulator. 
+To make it easy to locally test Lambda functions packaged as container images we open-sourced a lightweight web-server,
+Lambda Runtime Interface Emulator (RIE), which allows your function packaged as a container image to accept HTTP requests.
+You can install the [AWS Lambda Runtime Interface Emulator](https://github.com/aws/aws-lambda-runtime-interface-emulator) on your local machine to test your function.
+Thenm when you run the image function, you set the entrypoint to be the emulator. 
 
 *To install the emulator and test your Lambda function*
 
@@ -108,7 +114,8 @@ mkdir -p ~/.aws-lambda-rie && \
     curl -Lo ~/.aws-lambda-rie/aws-lambda-rie https://github.com/aws/aws-lambda-runtime-interface-emulator/releases/latest/download/aws-lambda-rie && \
     chmod +x ~/.aws-lambda-rie/aws-lambda-rie
 ```
-2) Run your Lambda image function using the docker run command. 
+
+1) Run your Lambda image function using the docker run command. 
 
 ```shell script
 docker run -d -v ~/.aws-lambda-rie:/aws-lambda -p 9000:8080 \
@@ -119,7 +126,7 @@ docker run -d -v ~/.aws-lambda-rie:/aws-lambda -p 9000:8080 \
 
 This runs the image as a container and starts up an endpoint locally at `http://localhost:9000/2015-03-31/functions/function/invocations`. 
 
-3) Post an event to the following endpoint using a curl command: 
+1) Post an event to the following endpoint using a curl command: 
 
 ```shell script
 curl -XPOST "http://localhost:9000/2015-03-31/functions/function/invocations" -d '{}'