chore(*): update plugin default options && add examples

Signed-off-by: storyicon <yuanchao@bilibili.com>

examples/greeter/README.md

@@ -0,0 +1,26 @@
+# Greeter
+
+This is the simplest grpc example, which does not reference any external grpc libraries.
+
+The following plug-ins are used:
+* [protoc-gen-go](google.golang.org/protobuf/cmd/protoc-gen-go)
+* [protoc-gen-go-grpc](google.golang.org/grpc/cmd/protoc-gen-go-grpc)
+
+You can compile the proto file in this directory by executing the following command:
+```
+powerproto build -r ./apis
+```
+
+Not surprisingly, you will get the following output:
+```
+➜ tree
+.
+├── README.md
+├── apis
+│   ├── greeter.pb.go
+│   ├── greeter.proto
+│   └── greeter_grpc.pb.go
+└── powerproto.yaml
+
+1 directory, 5 files
+```

examples/greeter/apis/greeter.proto

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+syntax = "proto3";
+
+package powerproto.examples.greeter;
+option go_package = "github.com/storyicon/powerproto/examples/greeter/apis;apis";
+
+service Greeter {
+    rpc SayHello (HelloRequest) returns (HelloReply);
+}
+
+message HelloRequest {
+    string name = 1;
+}
+
+message HelloReply {
+    string message = 1;
+}

examples/greeter/powerproto.yaml

@@ -0,0 +1,22 @@
+scopes:
+    - ./
+protoc: v3.17.3
+protocWorkDir: ""
+plugins:
+    protoc-gen-go: google.golang.org/protobuf/cmd/protoc-gen-go@v1.27.1
+    protoc-gen-go-grpc: google.golang.org/grpc/cmd/protoc-gen-go-grpc@v1.1.0
+repositories:
+    GOOGLE_APIS: https://github.com/googleapis/googleapis@75e9812478607db997376ccea247dd6928f70f45
+options:
+    - --go_out=.
+    - --go_opt=paths=source_relative
+    - --go-grpc_out=.
+    - --go-grpc_opt=paths=source_relative
+importPaths:
+    - .
+    - $GOPATH
+    - $POWERPROTO_INCLUDE
+    - $SOURCE_RELATIVE
+    - $GOOGLE_APIS/github.com/googleapis/googleapis
+postActions: []
+postShell: ""