To include an image, use the following:
{% include image.html file="<location of image relative to images/>" alt="alt text" caption="caption" %}
Note that you must always include a caption, even if it is empty.
For example, to link to the image $PATH_TO_GIT_REPO/images/sl_website-under-construction.jpeg
:

{% include image.html file="sl_website-under-construction.jpeg" alt="alt text" caption="" %}
To add an image in-line, like this →
, use:
{% include inline_image.html file="subfolder/Save.jpg" alt="Save button" %}