<docs> update en doc

docs/src/control/infrared.rst

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+.. _infrared:
+
+Enable IR and its adjustments function
+=======================================
+
+Using the ``SetOptionValue()`` function of the API, you can set various control values for the current open device.
+
+Enabling IR is setting ``Option::IR_CONTROL`` greater than 0. The greater the value, the greater the IR's intensity.
+
+.. Attention::
+  * mynteye s2100/s210a doesn't support this feature.
+
+Reference Code:
+
+.. code-block:: c++
+
+  auto &&api = API::Create(argc, argv);
+
+  // Detect infrared add-ons
+  LOG(INFO) << "Support infrared: " << std::boolalpha
+            << api->Supports(AddOns::INFRARED);
+  LOG(INFO) << "Support infrared2: " << std::boolalpha
+            << api->Supports(AddOns::INFRARED2);
+
+  // Get infrared intensity range
+  auto &&info = api->GetOptionInfo(Option::IR_CONTROL);
+  LOG(INFO) << Option::IR_CONTROL << ": {" << info << "}";
+
+  // Set infrared intensity value
+  api->SetOptionValue(Option::IR_CONTROL, 80);
+
+Reference running results on Linux:
+
+.. code-block:: bash
+
+  $ ./samples/_output/bin/tutorials/ctrl_infrared
+  I0504 16:16:28.016624 25848 utils.cc:13] Detecting MYNT EYE devices
+  I0504 16:16:28.512462 25848 utils.cc:20] MYNT EYE devices:
+  I0504 16:16:28.512473 25848 utils.cc:24]   index: 0, name: MYNT-EYE-S1000
+  I0504 16:16:28.512477 25848 utils.cc:30] Only one MYNT EYE device, select index: 0
+  I0504 16:16:28.520848 25848 infrared.cc:13] Support infrared: true
+  I0504 16:16:28.520869 25848 infrared.cc:15] Support infrared2: true
+  I0504 16:16:28.520889 25848 infrared.cc:20] Option::IR_CONTROL: {min: 0, max: 160, def: 0}
+
+At this point, if the image is displayed, you can see IR speckle on the image.
+
+.. attention::
+
+  The hardware will not record the IR value after being turned off. In order to keep IR enabled, you must set the IR value after turning on the device.
+
+Complete code samples，see `infrared.cc <https://github.com/slightech/MYNT-EYE-S-SDK/blob/master/samples/tutorials/control/infrared.cc>`_ .