Documentation for backgroundConfig

[TimUnderhay]

Thank you for the library!

I noticed that on the demo app that there are background config options but was unable to find any mention of them in the readme. I did find what I was looking for in the demo source code and TS definition.

Also, just FYI, the stackblitz example must be slightly behind as it does not have the background config options.

Cheers!

[llorenspujol]

You are welcome! :)

Thank you for the feedback! You are correct, backgroundConfig lacks documentation in the README.md. We should add it!

You are welcome to open a PR if you want.

About the Stackblitz example, it is way behind the current angular-grid-layout version, I should update it to the current version as soon I can.