cmd/go: update `go help mod edit` with the tool and ignore sections
The types were added to the docs, but not the fields in GoMod.
While here, I was initially confused about what is the top-level type
given that `type Module` comes first. Move `type GoMod` to the top
as it is the actual top-level type.
Change-Id: I1270154837501f5c7f5b21959b2841fd4ac808d0
Reviewed-on: https://go-review.googlesource.com/c/go/+/700116 Reviewed-by: Sean Liao <sean@liao.dev> Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Matloob <matloob@golang.org> Reviewed-by: Junyang Shao <shaojunyang@google.com>