Update timeout doc (#138)

Co-authored-by: Archit Aggarwal <architag@amazon.com>

docs/doxygen/timeouts.dox

@@ -11,6 +11,7 @@ The timeouts and the recommended configurations are listed below.
 4. [MQTT Receive Polling timeout](@ref mqtt_timeouts_receive_polling)
 5. [MQTT Send Retry timeout](@ref mqtt_timeouts_send_retry)
 6. [Timeouts for MQTT_ProcessLoop and MQTT_ReceiveLoop APIs](@ref mqtt_timeouts_process_receive_loop)
+7. [Timeout for MQTT_Connect](@ref mqtt_timeouts_connect)
 
 @section mqtt_timeouts_transport_send_receive Transport Send and Receive timeouts
 These are the network send and read operation blocking timeouts used by the implementation
@@ -39,10 +40,16 @@ This is to make sure that a Control packet including an MQTT ping request packet
 the Transport functions block for the maximum time. MQTT Keep Alive interval can be configured by setting the
 `keepAliveIntervalSec` member of the [MQTTContext_t](@ref mqtt_struct_types) structure.
 
+@see @ref mqtt_keepalive
+
 @section mqtt_timeouts_ping_response MQTT Ping Response timeout
 MQTT Ping Response timeout is the time to wait for a ping response to an MQTT ping request as part of the keep-alive
 mechanism in the MQTT Client. This timeout can be configured independent of the Transport timeouts unlike the MQTT Keep Alive
-interval, since a check for this timeout is done by coreMQTT library only after an attempt to receive from Transport layer.
+interval, since this timeout only depends on the MQTT broker, the platform and the network latencies.
+
+We recommend to choose a ping response timeout by experimenting with an MQTT application on a sample of devices and collecting the data
+of latency for each ping response from the broker after a ping request is sent. A timeout value can then be chosen based on the statistical
+measure suitable for the end application, such as 99th percentile or average.
 
 MQTT Ping Response timeout can be set by defining the configuration @ref MQTT_PINGRESP_TIMEOUT_MS.
 
@@ -88,7 +95,19 @@ being half way through a packet and will just error and disconnect if you don't
 That means, especially in multi-threaded application, the process loop timeout can be zero.
 
 @ref mqtt_processloop_function API can be used to manage the MQTT keep-alive mechanism and if used, application must invoke this API
-faster than the MQTT Keep Alive interval. If a dummy @ref MQTTGetCurrentTimeFunc_t was passed to @ref mqtt_init_function,
-then the timeout must be set to 0.
+faster than the MQTT Keep Alive interval. If a dummy @ref MQTTGetCurrentTimeFunc_t was passed to @ref mqtt_init_function, then the keep-alive mechanism is not supported by the @ref mqtt_processloop_function API; instead the @ref mqtt_receiveloop_function should be used.
+
+@see @ref mqtt_receivetimeout
+
+@section mqtt_timeouts_connect Timeout for MQTT_Connect
+This timeout is passed as an argument to @ref mqtt_connect_function. It is the maximum time to wait for an MQTT CONNACK packet. If this value is
+set to 0, then instead of a time-based loop, it will attempt to call the Transport Receive function up to a maximum number of retries,
+which is defined by @ref MQTT_MAX_CONNACK_RECEIVE_RETRY_COUNT.
+
+We recommend to choose a timeout for  @ref mqtt_connect_function by experimenting with an MQTT application on a sample of devices and
+collecting the data of latency for each CONNACK packet received from the broker after an MQTT CONNECT packet is sent. A timeout value can then be chosen
+based on the statistical measure suitable for the end application, such as 99th percentile or average.
+
+@see @ref mqtt_receivetimeout
 
 */