What you have should work with a default sphinx html build. The wrapping will occur based on text size and image size.
.. image:: path/to/image.png
:width: 200px
:align: left
very interesting paragraph about path/to/image.png
Will produce the following results, one with 200px width, and the other with 400px width. With text wrapping dependent on size.
Additional options are available. If the text takes up less vertical space than the image and you want to include the "clearfix" class you can insert custom html by using the raw directive.
.. raw:: html
<div class="clearfix">
.. image:: path/to/image.png
:width: 200px
:align: left
very interesting paragraph about path/to/image.png
.. raw:: html
</div>