add README in proto3 folder

# gPRC for mec013

The ETSI MEC ISG MEC013 Location API described using OpenAPI.

## Overview

These files were generated by the [OpenAPI Generator](https://openapi-generator.tech) project.

- API version: 3.1.1

- Package version: 

- Build package: org.openapitools.codegen.languages.ProtobufSchemaCodegen

For more information, please visit [https://forge.etsi.org/rep/mec/gs013-location-api](https://forge.etsi.org/rep/mec/gs013-location-api)

## Usage

Below are some usage examples for Python, Go and Ruby. For other languages, please refer to https://grpc.io/docs/quickstart/.

### Python

1. Install the grpcio-tools package

    ```sh

    $ pip install grpcio-tools

    ```

2. Create a directory for generated Python stubs

    ```sh

    $ mkdir python-stubs 

    ```

3. Run the following commands from the root of the directory containing this README that you are reading.

   - Models:

        ```sh

        $ python3 -m grpc_tools.protoc -I./proto3 --python_out=./python-stubs ./proto3/models/*

        ```

        The above command will generate .py files for all the data models in the ./models directory

   - Services:

        ```sh

        $ python3 -m grpc_tools.protoc -I./proto3 --python_out=./python-stubs --grpc_python_out=./python-stubs ./proto3/services/location_service.proto

        ```

        The above command will generate two files for the Location service:

        - _location_service_pb2.py_: containing the python data models used in the Location service file

        - _location_service_pb2_grpc.py_: containing all the classes and functions needed for the supported HTTP methods in the Location API

### Go

1. Install protocol buffer compiler

    ```sh

    $ apt install -y protobuf-compiler

    ```

2. Install Go plugins for `protoc`

    ```sh

    $ go install google.golang.org/protobuf/cmd/protoc-gen-go@v1.28.1

    ```

    ```sh

    $ go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@v1.2.0

    ```

3. Update `PATH` so `protoc` can find the plugins

    ```sh

    $ export PATH="$PATH:$(go env GOPATH)/bin"

    ```

4. Define a go package by appending `option go_package = "./mec013.services.locationservice";` in all .proto files like this:

    ```Go

    ...

    syntax = "proto3";

    package mec013.services.locationservice;

    option go_package = "./mec013.services.locationservice";

    import public "models/<xyz>.proto";

    ...

    ```

5. Generate Go code for models and services

    ```sh 

    $ mkdir go-stubs

    $ protoc --go_out=./go-stubs ./proto3/models/* -I./proto3

    $ protoc --go_out=./go-stubs ./proto3/services/* --go-grpc_out=go-stubs -I./proto3

    ```

    > The generated `<data_model>.pb.go` files will contain all the protocol buffer code to populate, serialize, and retrieve request and response message types defined in the `models` folder.

    > And the `location_service_grpc.pb.go` will contain the stubs for the methods defined in the `location_service.proto` file.

### Ruby

1. Install gRPC Ruby Plugin and required tools

   ```sh

   $ gem install grpc

   $ sudo apt install ruby-grpc-tools

   ```

2. Generate code

    ```sh

    $ mkdir ruby-stubs

    ```

    Run the following command to create Ruby modules for all the data models defined in the proto files.

    ```sh

    $ grpc_tools_ruby_protoc -I./proto3 --ruby_out=ruby-stubs ./proto3/models/*

    ```

    Run the following command to generate `location_service_pb.rb` and `location_service_services_pb.rb` files, containing stub and service classes for the endpoints and methods defined in MEC013 Location service.

    ```sh

    $ grpc_tools_ruby_protoc -I./proto3 --ruby_out=ruby-stubs --grpc_out=ruby-stubs ./proto3/services/*

    ```

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