Document how to use each plugin

[xela-95]

To facilitate the adoption of of gz-sim-yarp-plugins is useful to provide documentation on how to use and configure the plugins.

Hence, we want to add to each of them a brief README page documenting:

• how to add the plugin in a model;
• how to configure the plugin via yarpConfigurationString or yarpConfigurationFile, explaining what the required and optional parameters are;
• refer to the tutorials using it;

[traversaro]

In #232 I add a README for the new gzyarp::ConfigurationOverride plugin, I think we can use it as an example of the README.md to add to each plugin folder.

[xela-95]

Yes that is perfect to me! I will try to add the README for the other as soon as I have time!