github.webhook is missing field-level descriptions

[starpit]

in addition to adding some simple but helpful field-level descriptions. i suggest that we pioneer here a doclink field. this will be particularly helpful for the accessToken and events fields, which are quite cryptic on their own.

also, the main description field inaccurately renders GitHub as "github".

[starpit]

here is a suggestion of how it might look, where the `doclink`` fields are rendered as Learn More anchors.