Fix social preview icon

[MarkLodato]

I just pasted "slsa.dev" in Google Chat and the icon was Intel's!

Looks like we need to fix this somehow. I think this is called the "social preview" or "social card" or similar? I can't find much documentation, but https://metatags.io might be of some use.

We should also verify that the icon is correct on twitter, facebook, etc.

[inferno-chromium]

@devmoran - can you please help to fix this, would be simple for you than us debugging it.

[marcofranssen]

Most likely the og:… meta tags are missing.

https://ogp.me/

[devmoran]

Well caught! Will find some time to fix this tomorrow 👍

[MarkLodato]

Here's Twitter (link). Not bad, but we should prefix the tagline with "SLSA:".