add missing tutorial page (ros-perception#939)

This was supposed to be part of ros-perception#938

image_pipeline/doc/index.rst

@@ -30,6 +30,7 @@ stereo disparity images, and stereo point clouds. Components include:
 
    self
    camera_info
+   tutorials
    changelog
    camera_calibration <../camera_calibration/index.html#http://>
    depth_image_proc <../depth_image_proc/index.html#http://>

image_pipeline/doc/tutorials.rst

@@ -0,0 +1,26 @@
+Tutorials
+=========
+
+.. _`Remapping camera_info Topics`:
+
+Remapping camera_info Topics
+----------------------------
+When a ``camera_info`` topic is needed, an image_transport camera subscriber
+is typically used. ROS convention for naming ``camera_info`` topics is:
+
+ * **camera/image** - an image in namespace ``camera``.
+ * **camera/camera_info** - the associated camera info.
+
+So if a node subscribes to a topic called ``image``, and the user remaps this
+to ``my_camera/image``, then the associated camera info will be automatically
+remapped to ``mycamera/camera_info``.
+
+Most ROS 2 camera drivers will follow the convention, but occasionally they do
+not. In this case, you will have to manually remap the camera_info - but due
+to the way that ROS 2 remapping works you have to use the fully resolved
+camera info topic. An example:
+
+ * ``image`` is remapped to ``my_camera/image``.
+ * The fully resolved name for the camera info is now ``my_camera/camera_info``.
+ * If your camera driver actually publishes ``another_ns/camera_info``, then
+   you would have to remap ``my_camera/camera_info`` to ``another_ns/camera_info``.