Long lived URL

[jquevremont]

In section 5.3, the link to CV32E40X eXtension timing budget may change in the future, especially because it is an active project.

Therefore my suggestion is to copy the image in the document, or alternatively point to a long-lived GitHub URL.

The URL https://github.com/openhwgroup/core-v-verif/tree/master/lib/uvm_agents/uvma_cvxif could have the same issue if the repository is re-organized. I have no easy suggestion for it.

[christian-herber-nxp]

I will take the last known good commit hash to make these robust. If there are production releases, would be good to update to tagged versions.