[DOC] Some overlays are missing in the hero image of the README

[tbouffard]

The activity rounded by a red circle and the following sequence flow don't have overlays

Important

Be aware of #251 and #252.

Notes

The image has been first created with the script described in #45.
Then, it was recreated in #72 with the same script but store as SVG. This involves manual work to make the label be displayed at the right position (manually migrate foreignObject to SVG text). The SVG was finally cleaned in #78 (no visual change).

The easiest way to fix the overlay is to try to update the SVG directly and also provide an updated version of the script that would also generate it. That way, next time we will regenerate it, no overlays will miss.

See also #157