Updated Ubuntu instructions, added troubleshooting

Author: adamdbrw

README-UBUNTU.md

@@ -6,23 +6,24 @@ This readme contains information specific to Ubuntu 20.04. For general informati
 
 ### Prerequisites
 
-To prepare your machine for `ROS2 For Unity` build please follow step by step the `ros2cs` [Prequisites section](https://github.com/RobotecAI/ros2cs/blob/master/README-UBUNTU.md#prequisites).
-Prepairing environment with `ros2cs` instruction is ***crucial*** for failure-free Unity Asset generation.
-
-**Ommitting any of the steps mentioned above will result in a build failure!**
+Start with installation of dependencies. Make sure to complete each step of `ros2cs` [Prequisites section](https://github.com/RobotecAI/ros2cs/blob/master/README-UBUNTU.md#prequisites).
 
 ### Steps
 
 *  Clone this project.
 *  You need to source your ROS2 installation (`source /opt/ros/foxy/setup.bash`) before you proceed, for each new open terminal. It is convenient to include this command in your `~/.profile` file.
-*  Run `pull_repositories.sh`. This will pull `ros2cs` as well as your custom messages. You will be asked for gitlab credentials, so please fill your information.
+*  Run `pull_repositories.sh`. This will pull `ros2cs` as well as your custom messages. You might be asked for gitlab credentials. Remember to **pull this repository with each update** (e.g. with `vcs pull`).
 *  Run `build.sh` script.
     * You can build tests by adding `--with-tests` argument to `build` command.
     * It invokes `colcon_build` with `--merge-install` argument to simplify libraries installation.
     * It deploys built plugins into the Asset directory. Note that only plugins built for the current platform will be deployed (there is no cross-compilation).
     * It prepares Unity Asset that is ready to import into your Unity project.
 * Run `create_unity_asset.sh -u <your-path-to-unity-editor-executable>` to generate .unitypackage file in `install/unity_package`
 
+#### Troubleshooting
+
+If you see `"No ROS environment sourced. You need to source your ROS2 (..)"` message in Unity3D Editor, it means your environment was not sourced properly. This could happen if you run Unity but it redirects to Hub and ignores your console environment variables (this behavior can depend on Unity3D version). In such case, run project directly with `-projectPath` or add ros2 sourcing to your `~/.profile` file (you need to re-log for it to take effect). 
+
 ## OS-Specific usage remarks
 
 You can run Unity Editor or App executable from GUI (clicking) or from terminal as long as ROS2 is sourced in your environment.