doc/governance: updates based on 2024q4 election

https://vote.heliosvoting.org/helios/elections/e03494ce-e04c-41d0-bb05-ec5ccc632ce4/view

Question #1
    Update election requirements for Ceph Executive Council Elections?
        Remove "ranked-choice" requirement	13
        Keep "ranked-choice" requirement (no change)	16

Question #2
    Require periodic elections in governance charter?
        No (no change)	8
        Annual	15
        Semi-annual	3
        Quarterly	2

Question ceph#3
    Update the Ceph Executive Council term length?
        Change to 3 years	14
        Keep 2 years (no change)	14

Question ceph#4
    Amend governance document to require a supermajority of votes for amendments to the governance model? The current requirement is a simple majority.
        Require a supermajority	20
        Require a simple majority (no change)	9

Question ceph#5
    Clarify "supermajority" and "majority" election requirements?
        Of members voting on a given question (abstaining does not bias the vote)	18
        Of members voting on the election (abstaining is an implicit "no")	6
        Of members in the CSC	3

Signed-off-by: Patrick Donnelly <[email protected]>

doc/governance.rst

@@ -60,21 +60,25 @@ Responsibilities
 ----------------
 
  * Elect executive council
- * Amend governance model (by majority vote)
+ * Amend governance model by supermajority vote
  * Meet regularly to discuss and decide on tactical and strategic projects
    and improvements
+ * Hold an annual election
 
 Membership
 ----------
 
  * Developers, users, community members
- * Voting members can be nominated and added/removed by existing
-   members (2/3 majority)
+ * Members can be nominated and added/removed by existing members via a
+   supermajority vote
  * Anyone may attend steering committee meetings as a non-voting participant
  * Existing Ceph Leadership Team members are grandfathered in
  * Membership reflected by an email list and on the Ceph website and
    docs
 
+.. note:: A "supermajority" is a 2/3 majority of votes on a particular item
+          in an election. Abstaining does not bias a vote.
+
 Current Members
 ^^^^^^^^^^^^^^^