Figures and diagrams 

You can upload images in any folder below Documentation and use it like that:

Documentation/MyDocs.rst
..  figure:: /_Images/a4.jpg
    :alt: A spiral staircase seen from above, with people walking up and
        down the steps

    This is the image caption
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For details see Using images in reST documentation.

You can also use Embedded PlantUML diagrams.