Example tutorial for Pid

[awesomebytes]

Hello,

I made an example package/tutorial for the Pid class:

https://github.com/awesomebytes/control_toolbox_pid_tutorial

I find it a very reusable object (who wants to reimplement PIDs?) but I found it lacking documentation, as it took me a while to figure out how it actually works, specially, how to get the dynamic reconfigure running.

Let me know if you want to add that tutorial somwhere else. You may want to mention it on the README otherwise. Also, I'm far from a c++ expert, so from that point of view you may find weird/ugly stuff, I'm sure ;)