document .islink

Signed-off-by: Chris Warrick <kwpolska@gmail.com>

docs/manual.txt

@@ -1240,14 +1240,16 @@ Annotations require JQuery and are therefore not supported in the base theme.
 You can check bootstrap theme's ``base.html`` for details on how to handle them in
 custom themes.
 
-Image Galleries
----------------
+Images and Galleries
+--------------------
 
 To create an image gallery, all you have to do is add a folder inside ``galleries``,
 and put images there. Nikola will take care of creating thumbnails, index page, etc.
 
-If you click on images on a gallery, you should see a bigger image, thanks to
-the excellent `colorbox <http://www.jacklmoore.com/colorbox>`_
+If you click on images on a gallery, or on images with links in post, you will
+see a bigger image, thanks to the excellent `colorbox
+<http://www.jacklmoore.com/colorbox>`_.  If don’t want this behavior, add an
+``.islink`` class to your image or link.
 
 The gallery pages are generated using the ``gallery.tmpl`` template, and you can
 customize it there (you could switch to another lightbox instead of colorbox, change
@@ -1271,7 +1273,7 @@ The ``conf.py`` options affecting images and gallery pages are these::
     # {"source": "relative_destination"}. Images will be scaled down if necessary so
     # that neither width nor height is greater than MAX_IMAGE_SIZE and copied to
     # destination folder. A thumbnail will also be created in the same folder with
-    # ``.thumbnail`` inserted in the file name before the file extension
+    # ``.thumbnail`` inserted in the file name before the fileposts extension
     # (e.g. ``tesla.thumbnail.jpg``).
     IMAGE_FOLDERS = {'images': 'images'}
     # More image/gallery options: