Add cookbook item on creating custom content blocks

I would like to extend this cookbook item to include a configuration option e.g. for the album id, but I haven't figured out how to do that yet. I hope it's still useful.

I used the term "content block" throughout in the hopes of differentiating them from template blocks. I was wondering if another term would be more suitable. Perhaps it's already too late, but how about calling them something like "tiles" instead?