Add missing rootSlot documentation (#27709)

docs/src/developing/clients/jsonrpc-api.md

@@ -3266,6 +3266,7 @@ each containing an array of JSON objects with the following sub fields:
 - `commission: <number>`, percentage (0-100) of rewards payout owed to the vote account
 - `lastVote: <u64>` - Most recent slot voted on by this vote account
 - `epochCredits: <array>` - History of how many credits earned by the end of each epoch, as an array of arrays containing: `[epoch, credits, previousCredits]`
+- `rootSlot: <u64>` - Current root slot for this vote account
 
 #### Example:
 

rpc-client-api/src/response.rs

@@ -381,7 +381,7 @@ pub struct RpcVoteAccountInfo {
     /// Most recent slot voted on by this vote account (0 if no votes exist)
     pub last_vote: u64,
 
-    /// Current root slot for this vote account (0 if not root slot exists)
+    /// Current root slot for this vote account (0 if no root slot exists)
     pub root_slot: Slot,
 }