Clarify, or link to, info about filenames

[marcoscaceres]

The examples have different filenames (pr.yml, pr-push.yml) - presumedly, they have special meaning/side-effects.

It be great if the doc explained when to use which or pointed so some resource that explained those (or just chose the safest default one).

[marcoscaceres]

So, turns out the filename is meaningless, right? We (@plehegar and I) searched for uses of "spec-prod" action and found they use a bunch of different filenames.

I think "pr-push.yml" was the most popular. I'm still personally worried that this will confuse people (like me! I was already confused as I thought the name meant something).

I can live with "pr-push.yml" as the default one we use everywhere... but maybe a generic "action.yml" would be better, given how it behaves is defined in the .yml itself, and not related to the filename.

[sidvishnoi]

Should add a link to GitHub workflow syntax for details (missed in #69).

[marcoscaceres]

We are going with auto-publish.yml everywhere, but we should at least mention that the name is meaningless but we use it (or will use it) at the W3C to know if a spec is auto-published or not.