Expand org owner authority, remove ambiguities

- The "such as" wording left it open to ambiguity as to whether it's
  only the listed items or also others (while proper English would imply the
  latter, I meant the former when I wrote this originally)
- The former interpretation is unnecessarily restrictive, requiring
  further requests to increase authority whenever something new was
  being done.

This change makes it very explicit that it's an exclusive list for
individually-implementable changes (certain pre-approved changes and
minimal-impact changes), while leaving _all_ other non-controversial and
non-impactful changes up to the org owners, given two approvals.

doc/github-org-owners.md

@@ -18,29 +18,24 @@ For any GitHub-related needs, you can reach out to the org owners by either:
 This team's role is to manage and unblock users of the NixOS GitHub organization.
 The [Steering Committee (SC)](./governance.md) gives them autonomy to handle
 small day-to-day tasks and expects them to escalate bigger decisions.
+The following decision tree describes the org owners authority:
 
-All org owners can individually take care of implementing:
-- Decisions by bodies that have the authority to make GitHub org changes such as:
+**Is the change impactful or controversial?**
+- *Yes*: **Is the change pre-approved by a body with corresponding authority?** This includes:
   - Arbitrary decisions by the Steering Committee.
   - Moderation decisions by the moderation team.
   - Changes from approved RFCs.
-- Low-impact changes, such as:
+
+  - *Yes*: Any single org owner can implement it.
+  - *No*: Not within the org owners authority, should be escalated to the SC.
+- *No*: **Is the change one of the following?**
   - Adding new org members to allow review requests.
   - Creating new unprivileged Nixpkgs teams for mention.
   - Updating repository meta information.
-- Changes requested by a repository admin that have no impact outside their repository.
-
-Org owners need approval from at least one other org owner to take care of implementing
-higher-impact changes that are _not controversial_, such as:
-- Administer unmaintained repos, such as:
-  - Performing maintenance.
-  - Giving commit access to trusted people that offer maintenance.
-  - Archiving if appropriate.
-- Changes necessary to unblock automation.
-- Changes to the structure and CI of the [org repository](https://github.com/NixOS/org).
-- Content updates to the [GitHub organisation documentation](./github.md).
-
-Org owners have no authority to make other changes.
+  - Changes requested by a repository admin that have no impact outside their repository.
+
+  - *Yes*: Any single org owner can implement it.
+  - *No*: Approval from at least one other org owner is needed to implement it.
 
 ### Responsibilities