Approval voting guide changes (#2347)

* grab guide updates from approval-voting branch

* focus on control flow and behavior, not functions

* add approval voting preamble info

* tabs -> spaces

polkadot/roadmap/implementers-guide/src/runtime-api/candidate-events.md

@@ -5,11 +5,11 @@ Yields a vector of events concerning candidates that occurred within the given b
 ```rust
 enum CandidateEvent {
 	/// This candidate receipt was backed in the most recent block.
-	CandidateBacked(CandidateReceipt, HeadData),
+	CandidateBacked(CandidateReceipt, HeadData, CoreIndex, GroupIndex),
 	/// This candidate receipt was included and became a parablock at the most recent block.
-	CandidateIncluded(CandidateReceipt, HeadData),
+	CandidateIncluded(CandidateReceipt, HeadData, CoreIndex, GroupIndex),
 	/// This candidate receipt was not made available in time and timed out.
-	CandidateTimedOut(CandidateReceipt, HeadData),
+	CandidateTimedOut(CandidateReceipt, HeadData, CoreIndex),
 }
 
 fn candidate_events(at: Block) -> Vec<CandidateEvent>;

polkadot/roadmap/implementers-guide/src/runtime/inclusion.md

@@ -20,6 +20,7 @@ struct CandidatePendingAvailability {
   relay_parent_number: BlockNumber, // number of the relay-parent.
   backers: Bitfield, // one bit per validator, set for those who backed the candidate.
   backed_in_number: BlockNumber,
+  backing_group: GroupIndex,
 }
 ```
 

polkadot/roadmap/implementers-guide/src/types/overseer-protocol.md

@@ -63,6 +63,7 @@ enum ApprovalVotingMessage {
     /// Should not be sent unless the block hash is known.
     CheckAndImportAssignment(
         IndirectAssignmentCert,
+        CandidateIndex, // The index of the candidate included in the block.
         ResponseChannel<AssignmentCheckResult>,
     ),
     /// Check if the approval vote is valid and can be accepted by our view of the
@@ -509,6 +510,8 @@ enum RuntimeApiRequest {
     /// Get the contents of all channels addressed to the given recipient. Channels that have no
     /// messages in them are also included.
     InboundHrmpChannelsContents(ParaId, ResponseChannel<BTreeMap<ParaId, Vec<InboundHrmpMessage<BlockNumber>>>>),
+    /// Get information about the BABE epoch this block was produced in.
+    BabeEpoch(ResponseChannel<BabeEpoch>),
 }
 
 enum RuntimeApiMessage {