Add a little bit of documentation

[atar-axis]

trafficstars

Hey There! Thank you for publishing this project! Would you mind adding some documentstion in how to use it? That would be great for ROS beginners like me :)

[LoyVanBeek]

Just roslaunch node_alive server.launch and there should be some diagnostics published. If a node dies, you'll see it in the diagnostics.

If you want to ignore some nodes, add them to the parameter 'neglect_nodes.yaml`.

@Rayman @reinzor anything to add (besides a README) :smile: ?

[reinzor]

Feel free to add a README that describes the working principle and all parameters.

[Timple]

Note that rosmon also publishes diagnostics based on the nodes that are alive. Not sure which implementation is better, just mentioning an alternative for those who didn't know.

[Rayman]

If I read it correctly, rosmon is a replacement for roslaunch that does some additional monitoring. node_alive does only monitoring.

[CallumJHays]

@Timple Thanks for mentioning that! We already use rosmon so your comment has saved me a lot of work.