XX-3965 / Add file transfer connect client

fileTransferConnectClient/README.md

+# xxdk File Transfer Connect Example
+
+This mini-repository contains example logic for running a basic connection
+client and sending a file transfer. This is provided by the xx network team as a
+springboard to help consumers better understand our API and how it may be used.
+
+[`main.go`](main.go) contains the crux of the logic. We avoid complicating our
+example by avoiding the usage of CLI flags for basic variables you may change in
+the code. This file initiates an xxdk E2E object with a connection client built
+on top. Then the connection client is wrapped in a file transfer manager that
+facilitates the sending of an example file to a precanned contact object created
+in `fileTransferConnectServer`.
+
+[`utils.go`](utils.go) contains utility functions for running the program. In
+this case, we provide a tool initializing a log.
+
+## Build Instructions
+
+In these instructions we will go over building a connection client using our
+example. In order to build a client that successfully sends a message through
+the connection, we must first go over how to build and run a connection server.
+
+### Building a Client
+
+E2E clients communicate with each other directly via the xx network.
+
+To build and run a client, execute the following bash commands:
+```shell
+cd fileTransferConnectClient/
+go build -o client .
+./client 
+```
+
+This will start an e2e client and connection that can be monitored via log
+activity in `client.log`. This will read the contact at `connectServer.xxc.xxc`,
+attempting to establish a connection and send a test file. This functionality
+can be skipped by setting the relevant variable in the code to empty string.  
+
+By default, the client sends a single file to the recipient, with the recipient
+registering a `fileTransfer.ReceiveCallback` that listens to messages of type
+`catalog.NewFileTransfer` from the connection partner.
+
+Verification that the client is able to send messages may
+also be done. This can be done by checking the client's log for the string
+`Received progress callback for`.
+
+```shell
+grep "Received progress callback for" client.log 
+INFO 2022/07/07 12:59:12.088046 Received progress callback for...
+```
+
+