Transparency around funding

In his review @triblondon made the following comment:

> _Be transparent about funding_: Again to quote the blog: "This is real work, and we want to pay for it if it isn’t covered by your day job". Who is 'we' and where does that money come from? I suggest that all individuals who work on AMP for more than 50% of their working hours, should be disclosed and funding sources indicated.

Here's @cramforce's [initial answer](https://github.com/ampproject/meta/pull/1#issuecomment-422551537):

> Quick response on the funding side: We don't have this mapped out and it will depend on the individual requirements. What we have been discussing is for Google to fund an the [AMP OpenCollective project](https://opencollective.com/amp) out of which the AC would fund its members. With a transition to foundation this would then be taken over by it naturally.