Add comment describing fDisconnect behavior

src/net.h

@@ -689,6 +689,8 @@ public:
     bool m_limited_node{false}; //after BIP159, set by version message
     const bool fInbound;
     std::atomic_bool fSuccessfullyConnected{false};
+    // Setting fDisconnect to true will cause the node to be disconnected the
+    // next time DisconnectNodes() runs
     std::atomic_bool fDisconnect{false};
     // We use fRelayTxes for two purposes -
     // a) it allows us to not relay tx invs before receiving the peer's version message