[doc] Explain address handling logic in process messages

Co-authored-by: Suhas Daftuar <sdaftuar@gmail.com>

src/net_processing.cpp

@@ -2459,6 +2459,22 @@ void PeerLogicValidation::ProcessMessage(CNode& pfrom, const std::string& msg_ty
         }
 
         if (!pfrom.IsInboundConn() && !pfrom.IsBlockOnlyConn()) {
+            // For outbound peers, we try to relay our address (so that other
+            // nodes can try to find us more quickly, as we have no guarantee
+            // that an outbound peer is even aware of how to reach us) and do a
+            // one-time address fetch (to help populate/update our addrman). If
+            // we're starting up for the first time, our addrman may be pretty
+            // empty and no one will know who we are, so these mechanisms are
+            // important to help us connect to the network.
+            //
+            // We also update the addrman to record connection success for
+            // these peers (which include OUTBOUND_FULL_RELAY and FEELER
+            // connections) so that addrman will have an up-to-date notion of
+            // which peers are online and available.
+            //
+            // We skip these operations for BLOCK_RELAY peers to avoid
+            // potentially leaking information about our BLOCK_RELAY
+            // connections via the addrman or address relay.
             if (fListen && !::ChainstateActive().IsInitialBlockDownload())
             {
                 CAddress addr = GetLocalAddress(&pfrom.addr, pfrom.GetLocalServices());
@@ -2478,6 +2494,8 @@ void PeerLogicValidation::ProcessMessage(CNode& pfrom, const std::string& msg_ty
             m_connman.PushMessage(&pfrom, CNetMsgMaker(nSendVersion).Make(NetMsgType::GETADDR));
             pfrom.fGetAddr = true;
 
+            // Moves address from New to Tried table in Addrman, resolves
+            // tried-table collisions, etc.
             m_connman.MarkAddressGood(pfrom.addr);
         }