  In this addendum, we give a differential form interpretation of the proof of
the main theorem of arXiv:1812.02448, which gives lower bounds of the
dimensions of $\pi_k(B\mathrm{Diff}(D^4,\partial))\otimes\mathbb{Q}$ in terms
of the dimensions of Kontsevich's graph homology, and explain why it can be
extended to arbitrary even dimensions $d\geq 4$. We attempted to make the proof
accessible to more readers. Thus we do not assume familiarity with
configuration space integrals nor knowledge of finite type invariants. Part of
this addendum might be joined to the original article when it will be
re-submitted to the journal. This is not aimed at giving a correction to the
previous version.
