Update docs to reflect changed module namespace.

Signed-off-by: Rhys Mainwaring <[email protected]>

README.md

@@ -8,7 +8,7 @@ This project provides Python bindings for [`gz-msgs`](https://github.com/gazebos
 
 ### Install Gazebo
 
-Follow the installation instructions for [Gazebo Garden](https://gazebosim.org/docs/garden).
+Follow the installation instructions for [Gazebo Harmonic](https://gazebosim.org/docs/harmonic).
 This project depends directly on [`gz-msgs`](https://github.com/gazebosim/gz-msgs) and [`gz-transport`](https://github.com/gazebosim/gz-transport). These may be either available as system installs or in a source install in a local workspace folder which we assume is `~/gz_ws`.
 
 ### Install `gz-python`
@@ -29,10 +29,10 @@ export PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=python
 ```
 
 Set the environment variable determing the Gazebo version.
-The default is `garden`:
+The default is `harmonic`, although `garden` is also supported:
 
 ```bash
-export GAZEBO_VERSION=garden
+export GAZEBO_VERSION=harmonic
 ```
 
 Then create a build directory, configure and make:
@@ -46,23 +46,42 @@ make
 
 ### Update the Python environment
 
-Update the PYTHONPATH to include the location of the extension modules and the
-generated Python protobuf bindings.
+Update the `PYTHONPATH` to include the location of the extension modules:
 
 ```bash
 cd ~/gz_ws/src/gz-python
 export PYTHONPATH=${PYTHONPATH}:$(pwd)/build/python
 ```
 
+As `gz-msgs` now generates Python bindings for its `*.proto` definitions
+this project no longer generates them, so ensure that the `PYTHONPATH` also includes the path to the Gazebo Python bindings.  
+
+
 ## Usage
 
 ### `gz-msg` bindings 
 
 The Python bindings for `gz-msgs` are the standard generated protobuf code
-for Python. For example `gz-msgs/proto/gz/msgs/time.proto` may be used as follows: 
+for Python.
+
+Gazebo uses versioned module names, to use unversioned module names add the following before importing messages:
+
+```python
+import os
+
+# alias gz.msgs{GZ_MSGS_VER} to gz.msgs
+if os.environ["GZ_VERSION"] == "garden":
+    from gz import msgs9 as msgs
+elif os.environ["GZ_VERSION"] == "harmonic":
+    from gz import msgs10 as msgs
+else:
+    raise Exception(f"Invalid GZ_VERSION: {os.environ['GZ_VERSION']}")
+```
+
+In the remaining examples the unversioned imports for messages are assumed.
+For example `gz-msgs/proto/gz/msgs/time.proto` may be used as follows: 
 
 ```python
-# example.py
 from gz.msgs.time_pb2 import Time
 
 msg = Time()
@@ -73,7 +92,7 @@ print(msg)
 
 ### `gz-transport` bindings 
 
-The Python bindings for `gz-transport` are contained in a module called `transport`.
+The Python bindings for `gz-transport` are contained in a module called `gz.python.transport`.
 The object naming and usage for the most part follows the C++ interface,
 so the C++ Gazebo Tutorials are a good guide on how to use the library.
 
@@ -82,8 +101,8 @@ Publish:
 ```python
 from gz.msgs.stringmsg_pb2 import StringMsg
 
-from gz.transport import AdvertiseMessageOptions
-from gz.transport import Node
+from gz.python.transport import AdvertiseMessageOptions
+from gz.python.transport import Node
 
 # Create a transport node
 node = Node()
@@ -108,8 +127,8 @@ import typing
 
 from gz.msgs.stringmsg_pb2 import StringMsg
 
-from gz.transport import SubscribeOptions
-from gz.transport import Node
+from gz.python.transport import SubscribeOptions
+from gz.python.transport import Node
 
 def cb(msg: StringMsg) -> None:
     print("Msg: [{}] from Python".format(msg.data))
@@ -386,7 +405,7 @@ On macOS Bazel can be installed with `brew`:
 brew install bazel
 ```
 
-The [Google protocol buffers compiler](https://github.com/protocolbuffers/protobuf) version `3.19` is also required and can be installed with:
+The [Google protocol buffers compiler](https://github.com/protocolbuffers/protobuf) version `25.0` is also required and can be installed with:
 
 
 ```bash
@@ -502,11 +521,11 @@ py_binary(
 
 ### Protobuf compiler version
 
-The project depends on `protoc` version `3.19.1`. You must ensure that the version of `protoc` installed by `brew` matches (otherwise the examples will segfault).
+The project depends on `protoc` version `25.0`. You must ensure that the version of `protoc` installed by `brew` matches (otherwise the examples will segfault).
 
 ```bash
 $ protoc --version
-libprotoc 3.19.1
+libprotoc 25.0
 ```
 
 ### Protobuf generated Python libraries