add README

README.md

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+lambda-zig: A Custom Runtime for AWS Lambda
+===========================================
+
+This is a sample custom runtime built in zig. Simple projects will execute
+in <1ms, with a cold start init time of approximately 11ms.
+
+Some custom build steps have been added to build.zig:
+
+* `zig build iam`: Deploy and record a default IAM role for the lambda function
+* `zig build package`: Package the lambda function for upload
+* `zig build deploy`: Deploy the lambda function
+* `zig build run`: Run the lambda function
+
+Custom options:
+
+* **debug**: boolean flag to avoid the debug symbols to be stripped. Useful to see
+  error return traces in the AWS Lambda logs
+* **function-name**: set the name of the AWS Lambda function
+* **payload**: Use this to set the payload of the function when run using `zig build run`
+
+Additionally, a custom IAM role can be used for the function by appending ``-- --role myawesomerole``
+to the `zig build deploy` command. This has not really been tested. The role name
+is cached in zig-out/bin/iam_role_name, so you can also just set that to the full
+arn of your iam role if you'd like.
+
+The AWS Lambda function is compiled as a linux ARM64 executable. Since the build.zig
+calls out to the shell for AWS operations, you will need AWS CLI v2.2.43 or greater.
+
+This project vendors dependencies with [gyro](https://github.com/mattnite/gyro), so 
+first time build should be done with `gyro build`. This should be working
+on zig master - certain build.zig constructs are not available in zig 0.8.1.
+
+
+Caveats:
+
+* Small inbound lambda payloads seem to be confusing [requestz](https://github.com/ducdetronquito/requestz),
+  which just never returns, causing timeouts
+* Unhandled invocation errors seem to be causing the same problem