cdh:golang: Add README for cdh go client

Add README for cdh go client.

Signed-off-by: ChengyuZhu6 <chengyu.zhu@intel.com>

confidential-data-hub/golang/README.md

@@ -0,0 +1,63 @@
+# Confidential Data Hub Golang Client
+
+## Overview
+This offers a streamlined client interface for engaging with Confidential Data Hub (`CDH`) through both gRPC and TTRPC protocols. Used for integration into Go-based projects, it’s ideal for applications like the Node Resource Interface (`NRI`) or image verifiers plugins in containerd. Furthermore, it can be compiled into a client binary for direct interaction with `CDH`.
+
+## Getting Started
+
+### Usage as library
+
+Import the package into your Go project:
+
+```go
+//common interface
+import 	common "github.com/confidential-containers/guest-components/confidential-data-hub/golang/pkg/core"
+
+//grpc package 
+import cdhgrpcapi "github.com/confidential-containers/guest-components/confidential-data-hub/golang/pkg/grpc"
+//ttrpc package 
+import cdhttrpcapi "github.com/confidential-containers/guest-components/confidential-data-hub/golang/pkg/ttrpc"
+```
+
+Create a new client instance:
+
+```go
+//cdh grpc client
+c, err := cdhgrpcapi.CreateCDHGrpcClient("127.0.0.1:8043")
+
+//cdh ttrpc client
+c, err := cdhttrpcapi.CreateCDHTtrpcClient("/run/confidential-containers/cdh.sock")
+```
+
+Interact with `CDH` using the client, for example :
+```go
+unsealedValue, err := common.UnsealEnv(ctx, c, sealedSecret)
+```
+
+### Usage as binary
+
+Build and Install the binary, such as:
+```bash
+$ make RPC=grpc
+Building Go binaries...
+GOARCH=amd64 go build -o bin/cdh-go-client ./cmd/grpc-client
+$ sudo make install
+Installing binaries...
+install -D -m0755 bin/cdh-go-client /usr/local/bin
+```
+
+Interact with CDH using the binary, such as get sealed secret:
+```bash
+$ cdh-go-client -o UnsealSecret -I UnsealEnv -socket "127.0.0.1:8043" -i sealed.fakeheader.ewogICJ2ZXJzaW9uIjogIjAuMS4wIiwKICAidHlwZSI6ICJ2YXVsdCIsCiAgIm5hbWUiOiAia2JzOi8vL2RlZmF1bHQvdHlwZS90YWciLAogICJwcm92aWRlciI6ICJrYnMiLAogICJwcm92aWRlcl9zZXR0aW5ncyI6IHt9LAogICJhbm5vdGF0aW9ucyI6IHt9Cn0K.fakesignature
+Client rpc type: grpc
+unsealed value from env = that's the unsealed secret
+```
+or get sealed secret from file:
+```bash
+$ cat <<EOF > sealedsecretfile
+sealed.fakeheader.ewogICJ2ZXJzaW9uIjogIjAuMS4wIiwKICAidHlwZSI6ICJ2YXVsdCIsCiAgIm5hbWUiOiAia2JzOi8vL2RlZmF1bHQvdHlwZS90YWciLAogICJwcm92aWRlciI6ICJrYnMiLAogICJwcm92aWRlcl9zZXR0aW5ncyI6IHt9LAogICJhbm5vdGF0aW9ucyI6IHt9Cn0K.fakesignature
+EOF
+$ cdh-go-client -o UnsealSecret -I UnsealFile -socket "127.0.0.1:8043" -i sealedsecretfile 
+Client rpc type: grpc
+unsealed value from file = that's the unsealed secret
+```