Doc: Add alt-text for Qt Network examples

QDoc generates warnings for images that do not have an alternate-text
associated with it. Alt-text is required for to increase accessibilty
options.

This patch adds alt-text to images in the Qt Network

Fixes: QTBUG-135122
Pick-to: 6.9 6.8
Change-Id: I690f1d381ef5a9052e189dd1f3906243df557da0
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>

examples/network/doc/src/blockingfortuneclient.qdoc

@@ -9,7 +9,7 @@
     \ingroup examples-network
     \brief Demonstrates how to create a client for a network service.
 
-    \image blockingfortuneclient-example.png
+    \image blockingfortuneclient-example.png {The user provides server details and Q TcpSocket's blocking API is used to complete network operations}
 
     QTcpSocket supports two general approaches to network programming:
 

examples/network/doc/src/broadcastreceiver.qdoc

@@ -12,5 +12,5 @@
     This example uses the Qt Network APIs to demonstrate how to receive
     messages broadcasted over a local network.
 
-    \image broadcastreceiver-example.png
+    \image broadcastreceiver-example.png {The broadcast receiver listens for incoming messages using UDP communication}
 */

examples/network/doc/src/broadcastsender.qdoc

@@ -12,5 +12,5 @@
     This example uses Qt Network APIs to demonstrate how to broadcast messages
     to multiple clients over a local network.
 
-    \image broadcastsender-example.png
+    \image broadcastsender-example.png {The broadcast sender sends datagrams using UDP communication}
 */

examples/network/doc/src/dnslookup.qdoc

@@ -13,5 +13,5 @@
     name and print the results on the command line. As well as how you can
     use QCommandLineParser to parse command line arguments.
 
-    \image dnslookup-example.webp
+    \image dnslookup-example.webp {To perform a lookup, specify a host name and a type, then invoke the Q Dns Lookup lookup slot.}
 */

examples/network/doc/src/http.qdoc

@@ -13,7 +13,7 @@
     This example demonstrates how a simple HTTP client can fetch files
     from remote hosts.
 
-    \image http-example.webp
+    \image http-example.webp {The user enters the URL, file name, and download location in the main window. The QNetworkAccessManager class uses this information to download the file}
 
     The main work of this example is done in the HttpWindow class.
     Thus we will focus on that.

examples/network/doc/src/multicastsender.qdoc

@@ -12,5 +12,5 @@
     This example demonstrates how to send messages to the clients of a
     multicast group.
 
-    \image multicastsender-example.webp
+    \image multicastsender-example.webp {The application sends multicast messages via UDP communication}
 */

examples/network/doc/src/multistreamclient.qdoc

@@ -11,5 +11,5 @@
 
     This example demonstrates how to use SCTP, with multiple channels,
     to interact with other clients through a server.
-    \image multi-stream-client-example.webp
+    \image multi-stream-client-example.webp {The application allows the user to write data to other clients via SCTP communication}
 */

examples/network/doc/src/multistreamserver.qdoc

@@ -12,5 +12,5 @@
     This example demonstrates how to use SCTP, with multiple channels,
     on the server side, receiving multiple connections and sending
     messages to connected clients.
-    \image multi-stream-server-example.webp
+    \image multi-stream-server-example.webp {The application allows the user to write data to multiple clients via SCTP communication}
 */

examples/network/doc/src/network-chat.qdoc

@@ -12,5 +12,5 @@
     This example uses broadcasting with QUdpSocket and QNetworkInterface to
     discover its peers.
 
-    \image network-chat-example.webp
+    \image network-chat-example.webp {This application sets up a peer-to-peer network to allow multiple participants to chat with one another}
 */

examples/network/doc/src/rsslisting.qdoc

@@ -24,7 +24,7 @@
     the parsed content may start in one chunk of data but not be completed until
     a later chunk, requiring the parser to retain state between calls.
 
-    \image rsslisting.png
+    \image rsslisting.png {The application fetches information from the specified URL, in this case, Qt Blog, and then parses the available XML data}
 
     The main program is fairly minimal. It simply instantiates a \l QApplication
     and the \c RSSListing widget, shows the latter and hands over control to the

examples/network/doc/src/securesocketclient.qdoc

@@ -13,5 +13,5 @@
     encrypted connection, deal with authenticity problems, and display security
     and certificate information.
 
-    \image securesocketclient-example.webp
+    \image securesocketclient-example.webp {The user enters the host name and port that they want to connect to, and are then able to view the security certificate}
 */

examples/network/doc/src/threadedfortuneserver.qdoc

@@ -12,7 +12,7 @@
     simple network service that uses threads to handle requests from different
     clients. It is intended to be run alongside the Fortune Client example.
 
-    \image threadedfortuneserver-example.png
+    \image threadedfortuneserver-example.png {This application creates a server that can a separate thread for each client}
 
     The implementation of this example is similar to that of the
     \l{fortuneserver}{Fortune Server} example, but here we will

examples/network/doc/src/torrent.qdoc

@@ -11,5 +11,5 @@
     This example demonstrates some of the complex TCP/IP operations
     supported by the Qt Network APIs.
 
-    \image torrent-example.png
+    \image torrent-example.png {This application implements the BitTorrent protocol to facilitate peer-to-peer file-sharing}
 */

src/network/doc/src/examples.qdoc

@@ -7,7 +7,7 @@
     \title Network Examples
     \brief How to do network programming in Qt.
 
-    \image network-examples.webp
+    \image network-examples.webp {There are many examples that demonstrate the capabilities of Qt Network}
 
     Qt is provided with an extensive set of network classes to support both
     client-based and server side network programming.