Support for mardown

[revati-naik]

Describe the bug
A clear and concise description of what the bug is.

I have links to certain plantuml diagrams in my .rst file. The directive added in the conf.py file is .. uml::.

directive="uml", title="UML", prefix="UML_", color="#BFD8D2", style="node"

I use it in the `.rst file as

.. uml:: path_to_uml/file.puml

The extensions I use are sphinx-makrdown-builder and sphinxcontrib.plantuml

It works fine with HTML builder and I see the diagrams generated just right. In the markdown, I see empty blocks.

This is what my markdown looks like

<a id="UML_5EDCF"></a>

| UML: **path\_to\_uml/file.puml** [UML_5EDCF](#UML_5EDCF)  ![image](/home/$USERinternal_python_vendor_sphinx_needs/site-packages/sphinx_needs/images/feather_svg/arrow-down-circle.svg)![image](//home/$USER/internal_python_vendor_sphinx_needs/site-packages/sphinx_needs/images/feather_svg/arrow-right-circle.svg) <br/><br/>   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| <br/><br/><br/>                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |

Expected behavior
A clear and concise description of what you expected to happen

Markdown should be something like

plantuml source = path/to/uml/file.puml