Community: There should be a field in sigs.yaml for location of charter

[pmorie]

Currently the charter link is sprinkled into mission statement in many cases, while there is no first-class field for the location of a charter. We should add a first-class field for this information.

[nikhita]

Isn't the location of the charter of a sig always at community/sig-YOURSIG/charter.md? Ref: https://github.com/kubernetes/community/blob/master/committee-steering/governance/README.md#steps-to-create-a-sig-charter

[nikhita]

However, I guess it would be nice to mention the link to the charter in the sig readme though. Perhaps something like this in sig_readme.tmpl?

### Charter
The [charter](https://git.k8s.io/community/{{.Dir}}/charter.md) defines the scope and governance of SIG-{{.Name}}.

But most of the sigs don't have a charter right now so this would generate a 404 link. :(

[nikhita]

/kind feature

[cblecker]

/assign

[pmorie]

Isn't the location of the charter of a sig always at community/sig-YOURSIG/charter.md

A month or so ago, there wasn't a uniform term for this document that was in use. I think there are likely a couple different conventions in use. My own subjective opinion is that it's probably best to have an explicit field for this.

[carolynvs]

Making it a dedicated field will also help prompt people to fill it in. 😀

[cblecker]

Opened #2262 with this change.