update README with correct code generation procedure

.gitignore

 protoc/
 go-stubs/
-java-stubs/
+ruby-stubs/
 .proto-gen/
 python-stubs/
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proto3/README.md

@@ -12,21 +12,103 @@ For more information, please visit [https://forge.etsi.org/rep/mec/gs012-rnis-ap
 
 ## Usage
 
-Below are some usage examples for Go and Ruby. For other languages, please refer to https://grpc.io/docs/quickstart/.
+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/rni-service.proto
+        ```
+
+        The above command will generate two files for the RNI service:
+        - _rni_service_pb2.py_: containing the python data models used in the RNI service file
+        - _rni_service_pb2_grpc.py_: containing all the classes and functions needed for the supported HTTP methods in the RNI API
 
 ### Go
-```
-# 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/*
-```
+
+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@v1.26
+    ```
+    ```sh
+    $ go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@v1.1
+    ```
+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 = "./mec012";` in all .proto files like this:
+
+    ```Go
+    ...
+
+    syntax = "proto3";
+
+    package mec012;
+
+    option go_package = "./mec012";
+
+    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 `rni_service_grpc.pb.go` will contain the stubs for the methods defined in the `rni_service.proto` file.
+
 
 ### Ruby
-```
-# assuming `grpc_tools_ruby_protoc` has been installed via `gem install grpc-tools`
-RUBY_OUTPUT_DIR="/var/tmp/ruby/mec012"
-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/*
-```
+
+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 `rni_service_pb.rb` and `rni_service_services_pb.rb` files, containing stub and service classes for the endpoints and methods defined in MEC012 RNI service.
+
+    ```sh
+    $ grpc_tools_ruby_protoc -I./proto3 --ruby_out=ruby-stubs --grpc_out=ruby-stubs ./proto3/services/*
+    ```
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