Add @downloadurl and @updateurl

[JesperDramsch]

I added the @downloadurl and @updateurl meta pointing to the raw file in this repo.

Then Greasemonkey will be able to automatically check for updates every time.

Source: https://stackoverflow.com/questions/49393713/how-to-implement-auto-update-in-a-greasemonkey-script

[HatScripts]

Thanks! Merged and fixed typo (https://github.com/HatScripts/youtube-auto-liker/commit/2d30f43fdfd985f1e4a0f84770f1f0a93c575760).