Adding a regclient example

Signed-off-by: Brandon Mitchell <git@bmitch.net>

example_test.go

@@ -0,0 +1,48 @@
+package regclient_test
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/regclient/regclient"
+	"github.com/regclient/regclient/config"
+	"github.com/regclient/regclient/types/ref"
+)
+
+func ExampleNew() {
+	ctx := context.Background()
+	// use config.Host to provide registry logins, TLS, and other registry settings
+	exHostLocal := config.Host{
+		Name: "registry.example.org:5000",
+		TLS:  config.TLSDisabled,
+		User: "exUser",
+		Pass: "exPass",
+	}
+	exHostDH := config.Host{
+		Name: "docker.io",
+		User: "dhUser",
+		Pass: "dhPass",
+	}
+	// define a regclient with desired options
+	rc := regclient.New(
+		regclient.WithConfigHosts([]config.Host{exHostLocal, exHostDH}),
+		regclient.WithDockerCerts(),
+		regclient.WithDockerCreds(),
+		regclient.WithUserAgent("regclient/example"),
+	)
+	// create a reference for an image
+	r, err := ref.New("ghcr.io/regclient/regctl:latest")
+	if err != nil {
+		fmt.Printf("failed to create ref: %v\n", err)
+		return
+	}
+	defer rc.Close(ctx, r)
+	// get a manifest (or call other regclient methods)
+	m, err := rc.ManifestGet(ctx, r)
+	if err != nil {
+		fmt.Printf("failed to get manifest: %v\n", err)
+		return
+	}
+	fmt.Println(m.GetDescriptor().MediaType)
+	// Output: application/vnd.oci.image.index.v1+json
+}