Reorder and reword small portions of the keylength documentation and
make the ECC cert default explicitly stated in part 2 to avoid
confusion.
Fixes#6590
- Update openSUSE build badge file name (opensuse-leap.svg -> opensuse-leap-latest.svg)
- Update link target of build badge (letest -> acmetest), for item 1-12, 15, 16, 18, 19, 21
- Update Proxmox document link for 5.2 and later