CI : Added link_check

[PrathumP]

• Fixes issue CI: check if all links on docs website work once a day #83

[Anton-4]

Looks like we're missing an index.html for basic-cli, I'll try to fix that

[Anton-4]

roc-lang/roc#5655 will fix this

[Anton-4]

I fixed the index.html, but next the script found a /Documentation link that is broken, I'll look into that.
The script is already helping 😄

[PrathumP]

Yeah, I found out too that /documentation doesn't work.

[Anton-4]

I've made roc-lang/roc#5713 to fix the "/Documentation" link.