Add a link back from generated projects' READMEs

[armcknight]

Could be nice to put a "Generated by ..." link that leads to this repository, at the very bottom of the README template, so that generated projects can link back here for chain of knowledge and documentation.

Of course, it may be removed by people who would prefer not to leave it in, we could write a little message about it not being required but a nice thing to do.

[minimusic]

Since the whole project wasn't generated by our template, maybe we can use weaker attribution like "Project started with:" or similar?

[armcknight]

Sure, I just wanted a way to link back to this repo for people who don't know if exists, in case they want to change something in their project that originated here.