Update README file for proto generation

## Usage

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

Below are some code generation 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

        $ python -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

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

        ```

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

        - ue_identity_tag_info_service_pb2.py: containing the python data models used in the identity service file

        - ue_identity_tag_info_service_pb2_grpc.py: containing all the classes and functions needed for the supported HTTP methods in the UE-IDENTITY-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

    ```

# assuming `protoc-gen-go` has been installed with `go get -u github.com/golang/protobuf/protoc-gen-go`

mkdir /var/tmp/go/

protoc --go_out=/var/tmp/go/ services/*

protoc --go_out=/var/tmp/go/ models/*

    ```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 = "./mec014.services.Identityservice";` in all .proto files like this:

    ```Go

    ...

    syntax = "proto3";

    package mec033.services.IoTservice;

    option go_package = "./mec014.services.Identityservice";

    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 `ue_identity_tag_info_service_grpc.pb.go` will contain the stubs for the methods defined in the `ue_identity_tag_info_service.proto` file.

### Ruby

1. Install gRPC Ruby Plugin and required tools

   ```sh

   $ gem install grpc

   $ sudo apt install ruby-grpc-tools

   ```

# assuming `grpc_tools_ruby_protoc` has been installed via `gem install grpc-tools`

RUBY_OUTPUT_DIR="/var/tmp/ruby/mec014"

mkdir $RUBY_OUTPUT_DIR

grpc_tools_ruby_protoc --ruby_out=$RUBY_OUTPUT_DIR --grpc_out=$RUBY_OUTPUT_DIR/lib services/*

grpc_tools_ruby_protoc --ruby_out=$RUBY_OUTPUT_DIR --grpc_out=$RUBY_OUTPUT_DIR/lib models/*

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 `ue_identity_tag_info_service_pb2` and `ue_identity_tag_info_service_pb2_grpc` files, containing stub and service classes for the endpoints and methods defined in MEC033 IoT service.

    ```sh

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