Create sequence diagram for adding a backend tcp listener (#773)

Co-authored-by: Matthew Sandoval <mat24c@gmail.com>

docs/diagrams/AddListenerBackend.md

@@ -0,0 +1,73 @@
+```mermaid
+sequenceDiagram
+    participant Application
+    participant Netceptor
+    participant Netceptor closures
+    participant Netceptor connectInfo ReadChan
+    participant Netceptor connectInfo WriteChan
+    Application->>+Netceptor: New
+    Netceptor-->>-Application: netceptor instance n1
+    Application->>+Backend tcp.go: NewTCPListener
+    Backend tcp.go-->>-Application: backendsTCPListener b1
+    Application->>+Netceptor: AddBackend(b1)
+    Netceptor->>Netceptor: backendCancel(context)
+    Netceptor->>+Backend tcp.go:(Backend Interface) b1.Start(context, waitgroup)
+    Backend tcp.go->>+Backend utils.go:listenerSession(context, waitgroup, logger, ListenFunc, AcceptFunc, CancelFunc)
+    Backend utils.go->>+Backend tcp.go:ListenFunc()
+    Backend tcp.go-->>-Backend utils.go:error
+    Backend utils.go->>Backend utils.go:create chan BackendSession
+    Backend utils.go-)+Backend sessChan Closure:go closure
+    loop Every time AcceptFunc is called
+        Backend sessChan Closure->>Backend sessChan Closure:AcceptFunc
+    end
+    
+    Backend utils.go-->>-Backend tcp.go:chan (Backend Interface) BackendsSession
+    Backend tcp.go-->>-Netceptor: chan (Backend Interface) BackendsSession
+    Netceptor->>+Netceptor closures: go closure
+    Netceptor closures->>+Netceptor closures: go closure
+    Netceptor closures->>Netceptor closures: runProtocol(context, backend session, backendInfo)
+    Netceptor closures->>+Netceptor connectInfo ReadChan: make (chan []byte)
+    Netceptor closures->>+Netceptor connectInfo WriteChan: make (chan []byte)
+    Netceptor closures-)Netceptor closures: protoReader(backend session)
+    loop 
+        Backend sessChan Closure->>Netceptor closures: sess.Recv(1 * time.Second)
+        Netceptor closures->>Netceptor connectInfo ReadChan: ci.ReadChan <- buf
+    end
+    loop 
+        Netceptor connectInfo WriteChan->>Netceptor closures: message, more = <-ci.WriteChan
+        Netceptor closures->>Backend sessChan Closure: sess.Send(message)
+    end
+    Netceptor closures-)Netceptor closures: protoWriter(backend session)
+    Netceptor closures-)+Netceptor closures: s.sendInitialConnectMessage(ci, initDoneChan)
+    Netceptor closures-)Netceptor closures: s.translateStructToNetwork(MsgTypeRoute, s.makeRoutingUpdate(0))
+    Netceptor closures-)-Netceptor closures: context.Done()
+    Netceptor connectInfo ReadChan->>Netceptor closures: data = <-ci.ReadChan
+    alt established
+        alt MsgTypeData
+            Netceptor closures->>Netceptor closures: translateDataToMessage(data []byte)
+        else MsgTypeRoute
+            Netceptor closures->>Netceptor closures: s.handleRoutingUpdate(ri, remoteNodeID)
+        else MsgTypeServiceAdvertisement
+            Netceptor closures->>Netceptor closures: s.handleServiceAdvertisement(data, remoteNodeID)
+        else MsgTypeReject
+            Netceptor closures->>Netceptor closures: return error
+        end
+    else !established
+        alt msgType == MsgTypeRoute
+            Netceptor closures->>Netceptor closures: add connection
+        else msgType == MsgTypeReject
+            Netceptor closures->>Netceptor closures: return error
+        end
+    end
+    
+    Netceptor closures->>Netceptor connectInfo WriteChan: ci.WriteChan <- ConnectMessage
+    Netceptor closures->>-Netceptor closures: wg Done()
+    Backend sessChan Closure->>Backend sessChan Closure:CancelFunc
+    Backend sessChan Closure-->>-Application:context.Done()
+    Netceptor->>Netceptor closures: wg Done()
+    Netceptor closures-->>-Netceptor: 
+    Netceptor connectInfo ReadChan-->>-Netceptor closures: context.Done()
+    Netceptor connectInfo WriteChan-->>-Netceptor closures: context.Done()
+
+```
+