feat: Add README for net (#706)

* feat: Add README for net

Author: ajewellamz

DynamoDbEncryption/runtimes/net/README.md

@@ -0,0 +1,112 @@
+## DynamoDbEncryption
+
+This project implements the AWS Database Encryption SDK for DynamoDB for .NET.
+
+[Security issue notifications](./CONTRIBUTING.md#security-issue-notifications)
+
+## Using the AWS Database Encryption SDK for DynamoDB for .NET
+
+The AWS Database Encryption SDK for DynamoDB is available on [NuGet](https://www.nuget.org/) and can referenced from an existing `.csproj` through typical ways.
+
+Using the dotnet CLI:
+```shell
+dotnet add <your-project-name>.csproj package AWS.Cryptography.DbEncryptionSDK.DynamoDb
+```
+
+Alternatively, you may directly modify the `.csproj` and add the AWS Database Encryption SDK for DynamoDB to `PackageReference` `ItemGroup`:
+```xml
+<PackageReference Include="AWS.Cryptography.DbEncryptionSDK.DynamoDb" />
+```
+
+The AWS Database Encryption SDK for DynamoDB targets [.NET](https://learn.microsoft.com/en-us/dotnet/fundamentals/implementations#net-5-and-later-versions) 6.0
+and newer on all platforms,
+and [.NET Framework](https://docs.microsoft.com/en-us/dotnet/framework/) 4.8.0 and newer on Windows only.
+
+### Additional setup for macOS only
+
+If you are using macOS then you must install OpenSSL 1.1,
+and the OpenSSL 1.1 `lib` directory must be on the dynamic linker path at runtime.
+Also, if using an M1-based Mac, you must install OpenSSL and the .NET SDK for x86-64.
+Please refer to [the wiki](https://github.com/aws/aws-encryption-sdk-dafny/wiki/Using-the-AWS-Encryption-SDK-for-.NET-on-macOS) for detailed instructions.
+
+## Building the AWS Database Encryption SDK for DynamoDB for .NET
+
+To build, the AWS Database Encryption SDK for DynamoDB requires the most up to date version of [Dafny](https://github.com/dafny-lang/dafny) on your PATH.
+
+The AWS Database Encryption SDK for DynamoDB targets frameworks [`net48` and `net6.0`](https://docs.microsoft.com/en-us/dotnet/standard/frameworks#supported-target-frameworks).
+To build and test the AWS Database Encryption SDK for DynamoDB, you must install the following .NET tools:
+
+* [.NET 6.0](https://dotnet.microsoft.com/en-us/download/dotnet/6.0) or newer
+* [.NET Framework 4.8.0](https://docs.microsoft.com/en-us/dotnet/framework/install/) or newer (if on Windows)
+
+You will also need to ensure that you fetch all submodules using either `git clone --recursive ...` when cloning the repository or `git submodule update --init` on an existing clone.
+
+To build all source files into one dll:
+
+```
+# Transpile Dafny to .NET
+cd DynamoDbEncryption
+make transpile_implementation_net
+# Run dotnet restore
+make setup_net
+# Run dotnet build
+dotnet build runtimes/net
+```
+
+### (Optional) Set up the AWS Database Encryption SDK for DynamoDB to work with AWS KMS
+
+If you set up the AWS Database Encryption SDK for DynamoDB to use the AWS KMS Keyring,
+the AWS Database Encryption SDK for DynamoDB will make calls to AWS KMS on your behalf,
+using the appropriate AWS SDK.
+
+However, you must first set up AWS credentials for use with the AWS SDK. 
+Instructions for setting up AWS credentials are available in the [AWS Docs for the AWS SDK for .NET.](https://docs.aws.amazon.com/sdk-for-net/v3/developer-guide/net-dg-config-creds.html).
+
+## Testing the AWS Database Encryption SDK for DynamoDB for .NET
+
+### Configure AWS credentials
+
+To run the test suite you must first set up AWS credentials for use with the AWS SDK.
+This is required in order to run the integration tests, which use a KMS Keyring against a publicly accessible KMS CMK.
+
+Instructions for setting up AWS credentials are available in the [AWS Docs for the AWS SDK for .NET](https://docs.aws.amazon.com/sdk-for-net/v3/developer-guide/net-dg-config-creds.html).
+
+### Run the tests
+
+Run the test suite with:
+
+```
+cd DynamoDbEncryption
+make transpile_test_net
+# Windows/Linux
+make test_net 
+# On Mac
+make test_net_mac_brew
+```
+
+Run tests on examples, to ensure they are up to date:
+
+```
+cd Examples
+make transpile_net
+cd runtimes/net
+dotnet run
+```
+
+Please note that tests and test vectors require internet access and valid AWS credentials, since calls to KMS are made as part of the test workflow.
+
+## Other Development advice
+
+Most c# IDEs appreciate Solution files.
+To generate one Solution file for all the projects here,
+run:
+```
+cd DynamoDbEncryption/runtimes/net
+dotnet new sln --name DBESDK
+dotnet sln add $(find . -name '*.csproj')
+```
+Then ask your IDE to open `DBESDK.sln`.
+
+## License
+
+This library is licensed under the Apache 2.0 License.