add back generator

cmd/protoc-gen-micro/README.md

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+# protoc-gen-micro
+
+This is protobuf code generation for go-micro. We use protoc-gen-micro to reduce boilerplate code.
+
+## Install
+
+```
+go install github.com/micro/go-micro/cmd/protoc-gen-micro
+```
+
+Also required: 
+
+- [protoc](https://github.com/google/protobuf)
+- [protoc-gen-go](https://google.golang.org/protobuf)
+
+## Usage
+
+Define your service as `greeter.proto`
+
+```
+syntax = "proto3";
+
+package greeter;
+option go_package = "/proto;greeter";
+
+service Greeter {
+	rpc Hello(Request) returns (Response) {}
+}
+
+message Request {
+	string name = 1;
+}
+
+message Response {
+	string msg = 1;
+}
+```
+
+Generate the code
+
+```
+protoc --proto_path=. --micro_out=. --go_out=. greeter.proto
+```
+
+Your output result should be:
+
+```
+./
+    greeter.proto	# original protobuf file
+    greeter.pb.go	# auto-generated by protoc-gen-go
+    greeter.micro.go	# auto-generated by protoc-gen-micro
+```
+
+The micro generated code includes clients and handlers which reduce boiler plate code
+
+### Server
+
+Register the handler with your micro server
+
+```go
+type Greeter struct{}
+
+func (g *Greeter) Hello(ctx context.Context, req *proto.Request, rsp *proto.Response) error {
+	rsp.Msg = "Hello " + req.Name
+	return nil
+}
+
+proto.RegisterGreeterHandler(service.Server(), &Greeter{})
+```
+
+### Client
+
+Create a service client with your micro client
+
+```go
+client := proto.NewGreeterService("greeter", service.Client())
+```
+
+### Errors
+
+If you see an error about `protoc-gen-micro` not being found or executable, it's likely your environment may not be configured correctly. If you've already installed `protoc`, `protoc-gen-go`, and `protoc-gen-micro` ensure you've included `$GOPATH/bin` in your `PATH`.
+
+Alternative specify the Go plugin paths as arguments to the `protoc` command
+
+```
+protoc --plugin=protoc-gen-go=$GOPATH/bin/protoc-gen-go --plugin=protoc-gen-micro=$GOPATH/bin/protoc-gen-micro --proto_path=. --micro_out=. --go_out=. greeter.proto
+```
+
+### Endpoint
+
+Add a micro API endpoint which routes directly to an RPC method
+
+Usage:
+
+1. Clone `github.com/googleapis/googleapis` to use this feature as it requires http annotations.
+2. The protoc command must include `-I$GOPATH/src/github.com/googleapis/googleapis` for the annotations import.
+
+```diff
+syntax = "proto3";
+
+package greeter;
+option go_package = "/proto;greeter";
+
+import "google/api/annotations.proto";
+
+service Greeter {
+	rpc Hello(Request) returns (Response) {
+		option (google.api.http) = { post: "/hello"; body: "*"; };
+	}
+}
+
+message Request {
+	string name = 1;
+}
+
+message Response {
+	string msg = 1;
+}
+```
+
+The proto generates a `RegisterGreeterHandler` function with a [api.Endpoint](https://godoc.org/go-micro.dev/v3/api#Endpoint). 
+
+```diff
+func RegisterGreeterHandler(s server.Server, hdlr GreeterHandler, opts ...server.HandlerOption) error {
+	type greeter interface {
+		Hello(ctx context.Context, in *Request, out *Response) error
+	}
+	type Greeter struct {
+		greeter
+	}
+	h := &greeterHandler{hdlr}
+	opts = append(opts, api.WithEndpoint(&api.Endpoint{
+		Name:    "Greeter.Hello",
+		Path:    []string{"/hello"},
+		Method:  []string{"POST"},
+		Handler: "rpc",
+	}))
+	return s.Handle(s.NewHandler(&Greeter{h}, opts...))
+}
+```
+
+## LICENSE
+
+protoc-gen-micro is a liberal reuse of protoc-gen-go hence we maintain the original license