[template] Adds a Tentative Deliverables section

[plehegar]

This adds support in the charter template to list specifications that are being incubated but may get adopted later without rechartering.

[tantek]

This looks like a reasonable placeholder to me. I'm curious what @cwilso thinks (per the AB's Incubation priority project).

[csarven]

I think this section should briefly clarify/qualify what constitutes "incubation" with reference to existing W3C guide/recommendation. Along the lines of #262 (comment) , e.g.,:

The Working Group will adopt proposals that fulfill the requirements of W3C Recommendation Track Readiness [..] Proposals can be made to the Working Group through W3C Community Groups or another similar incubation phase.

It tries to ensure (or at least raises awareness about the common understanding) to some extent that incubation was achieved in a space that followed the principles of open standards development. This is to contrast "incubation" that may be done in private-space and to avoid potential rubber-stamping later on.

[hober]

This looks good to me. I like that it's pretty general, and doesn't presume that all incubations are done in WICG, or a W3C Community Group for that matter.

[tantek]

agree with @cwilso's comments, and would like to see changes in this PR accordingly