docs: replenish config/apollo and registry/discovery readme (#1625)

* docs(config/apollo): replenish config/apollo readme

* docs(registry/discovery): replenish registry/discovery readme

* docs: complete docs of config/apollo and registry/discovery

contrib/config/apollo/README.md

@@ -0,0 +1,104 @@
+## Apollo config centry
+
+This module implements the `config.Source` interface in kratos based apollo config management center.
+
+[![go.dev reference](https://img.shields.io/badge/go.dev-reference-007d9c?logo=go&logoColor=white&style=flat-square)](https://pkg.go.dev/github.com/go-kratos/kratos/contrib/config/apollo/v2)
+
+### Quick start
+
+```go
+import (
+	"fmt"
+	"log"
+
+	"github.com/go-kratos/kratos/contrib/config/apollo/v2"
+	"github.com/go-kratos/kratos/v2/config"
+)
+
+func main() {
+	c := config.New(
+		config.WithSource(
+			apollo.NewSource(
+				apollo.WithAppID("kratos"),
+				apollo.WithCluster("dev"),
+				apollo.WithEndpoint("http://localhost:8080"),
+				apollo.WithNamespace("application,event.yaml,demo.json"),
+				apollo.WithEnableBackup(),
+				apollo.WithSecret("ad75b33c77ae4b9c9626d969c44f41ee"),
+			),
+		),
+	)
+	var bc bootstrap
+	if err := c.Load(); err != nil {
+		panic(err)
+	}
+	
+	// use value and watch operations，help yourself. 
+}
+```
+
+### Options list
+
+> You get what you see.
+
+```go
+// specify the app id
+func WithAppID(appID string) Option
+// specify the cluster of application
+func WithCluster(cluster string) Option
+
+// enable backup or not, and where to back up them.
+func WithBackupPath(backupPath string) Option
+func WithDisableBackup() Option
+func WithEnableBackup() Option
+
+// specify apollo endpoint, such as http://localhost:8080
+func WithEndpoint(endpoint string) Option
+
+// inject a logger to debug
+func WithLogger(logger log.Logger) Option
+
+// namespaces to load, comma to separate. 
+func WithNamespace(name string) Option
+
+// secret is the apollo secret key to access application config.
+func WithSecret(secret string) Option
+```
+
+### Notice
+
+apollo config center use `Namespace` to be part of the key. For example:
+
+***application.json***
+
+```json
+{
+  "http": {
+    "address": ":8080",
+    "tls": {
+      "enable": false,
+      "cert_file": "",
+      "key_file": ""
+    }
+  }
+}
+```
+
+you got them in kratos config instance maybe look like:
+
+```go
+config := map[string]interface{}{
+	// application be part of the key path.
+	"application": map[string]interface{}{
+        "http": map[string]interface{}{
+            "address": ":8080",
+            "tls": map[string]interface{}{
+                "enable": false,
+                "cert_file": "",
+                "key_file": ""
+            }
+        }
+    }
+}
+_ = config
+```

contrib/registry/discovery/README.md

@@ -1,4 +1,97 @@
-# Discovery Registry
+## Discovery Registry 
 
-## [discovery](https://github.com/bilibili/discovery)
+This module implements a `registry.Registrar` and `registry.Discovery` interface in kratos based `bilibili/discovery`.
+
+[![go.dev reference](https://img.shields.io/badge/go.dev-reference-007d9c?logo=go&logoColor=white&style=flat-square)](https://pkg.go.dev/github.com/go-kratos/kratos/contrib/registry/discovery/v2)
+
+### Quick Start
+
+**_Register a service_**
+
+```go
+import (
+	"github.com/go-kratos/kratos/contrib/registry/discovery/v2"
+)
+
+func main() {
+	logger := log.NewStdLogger(os.Stdout)
+	logger = log.With(logger, "service", "example.registry.discovery")
+	
+	// initialize a registry
+	r := discovery.New(&discovery.Config{
+		Nodes:  []string{"0.0.0.0:7171"},
+		Env:    "dev",
+		Region: "sh1",
+		Zone:   "zone1",
+		Host:   "hostname",
+	}, logger)
+
+	// construct srv instance
+	// ...
+	
+	app := kratos.New(
+		kratos.Name("helloworld"),
+		kratos.Server(
+			httpSrv,
+			grpcSrv,
+		),
+		kratos.Metadata(map[string]string{"color": "gray"}),
+		// use Registrar
+		kratos.Registrar(r),
+	)
+	
+	if err := app.Run(); err != nil {
+		log.NewHelper(logger).Fatal(err)
+	}	
+}
+```
+
+**_Discover a service_**
+
+```go
+import (
+	"github.com/go-kratos/kratos/contrib/registry/discovery/v2"
+	"github.com/go-kratos/kratos/v2/transport/grpc"
+)
+
+func main() {
+	// initialize a discovery
+	r := discovery.New(&discovery.Config{
+		Nodes:  []string{"0.0.0.0:7171"},
+		Env:    "dev",
+		Region: "sh1",
+		Zone:   "zone1",
+		Host:   "localhost",
+	}, nil)
+
+	conn, err := grpc.DialInsecure(
+		context.Background(),
+		grpc.WithEndpoint("discovery:///appid"),
+		// use discovery
+		grpc.WithDiscovery(r),
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer conn.Close()
+	
+	// request and log
+}
+```
+
+### Config explain
+
+```go
+type Config struct {
+	Nodes  []string // discovery nodes address
+	Region string   // region of the service, sh
+	Zone   string   // zone of region, sh001
+	Env    string   // env of service, dev, prod and etc
+	Host   string   // hostname of service
+}
+```
+
+### References 
+
+- [bilibili/discovery](https://github.com/bilibili/discovery)