DOC: Document that ImageRegionIterator constructors initialize at begin

Explicitly specify that those constructors initialize the iterator at the begin of the region.

Author: N-Dekker

Modules/Core/Common/include/itkImageRegionConstIterator.h

@@ -146,8 +146,8 @@ class ITK_TEMPLATE_EXPORT ImageRegionConstIterator : public ImageConstIterator<T
     m_SpanEndOffset = 0;
   }
 
-  /** Constructor establishes an iterator to walk a particular image and a
-   * particular region of that image. */
+  /** Constructor establishes an iterator to walk a particular image and a particular region of that image. Initializes
+   * the iterator at the begin of the region. */
   ImageRegionConstIterator(const ImageType * ptr, const RegionType & region)
     : ImageConstIterator<TImage>(ptr, region)
   {

Modules/Core/Common/include/itkImageRegionIterator.h

@@ -99,8 +99,8 @@ class ITK_TEMPLATE_EXPORT ImageRegionIterator : public ImageRegionConstIterator<
   /** Default constructor. Needed since we provide a cast constructor. */
   ImageRegionIterator() = default;
 
-  /** Constructor establishes an iterator to walk a particular image and a
-   * particular region of that image. */
+  /** Constructor establishes an iterator to walk a particular image and a particular region of that image. Initializes
+   * the iterator at the begin of the region. */
   ImageRegionIterator(ImageType * ptr, const RegionType & region);
 
   /** Constructor that can be used to cast from an ImageIterator to an