Use img tag instead of markdown

PyPI doesn't seem to show SVG image. We're hoping that this might fix it.

Author: mhxion

README.md

@@ -9,7 +9,7 @@ the [University Computing Centre](https://www.urz.uni-heidelberg.de/en)
 [eLabFTW API documentation](https://doc.elabftw.net/api/v2/) with ease. elAPI provides a simple interface via its CLI
 executable, and numerous advanced APIs when it is used directly as a Python package.
 
-![elAPI features in a nutshell](./.assets/elapi_features.svg)
+<img src="./.assets/elapi_features.svg" alt="elAPI features in a nutshell" />
 
 **Example:**