Hpc - Guide update : limitation VCD, vcd network, spec hpc

[pg-ovh]

3 guide update FR version draft.

[Y0Coss]

II see there's no real update on the /hpc_limits/ guide, outside of getting rid of the compact mode, which is debatable. The date should not be updated for the guide if no content is updated.

[Y0Coss]

I reverted the hierarchy of the /vcd-get-concepts/ guide as there is no need for numbered steps considering it's a concepts page. For this concept guide, we chose to have H2 (no H3) parts to avoid all the steps being dependent from the ## Objective