Update README.md with code generation instructions

Author: carbolymer

cardano-rpc/README.md

@@ -2,7 +2,7 @@
 
 ## What's this
 
-The `cardano-rpc` package provides client and server haskell modules for gRPC interface of `cardano-node`. 
+The `cardano-rpc` package provides client and server haskell modules for gRPC interface of `cardano-node`.
 It implements [UTxO RPC](https://utxorpc.org/introduction) protobuf communication protocol specification.
 
 ## Building
@@ -14,7 +14,24 @@ You need the following dependencies installed on your system:
 - [`snappy`](https://github.com/google/snappy) development files (`libsnappy-dev` in Ubuntu)
 - [`protobuf`](https://developers.google.com/protocol-buffers/) compiler (`protobuf-compiler` in Ubuntu)
 
-Then do:
+### Generating the Haskell code from proto definitions
+
+You need to install `buf` and `proto-lens-protoc`.
+1. Follow the `buf` installation guide at: https://buf.build/docs/cli/installation/
+1. To install Haskell protobuf code compiler:
+  ```bash
+  cabal install proto-lens-protoc
+  ```
+
+1. Generate Haskell code using:
+  ```bash
+  ( cd cardano-rpc/ ; buf generate proto )
+  ```
+  This will output the generated Haskell code into `cardano-rpc/gen` directory.
+
+### Building the haskell code
+
+To build the package use the following command:
 ```bash
 cabal build cardano-rpc
 ```