readme: updated docs links to point to version 4.0 (#8415)
readme: updated docs links to point to version 4.0 (#8415)

Signed-off-by: Matthieu Vachon <f2462a2b30e0847282041784cd8e50eac68020cb@gmail.com>
pingcap/tikv,BusyJay/tikv,BusyJay/tikv,c4pt0r/tikv,BusyJay/tikv,pingcap/tikv,BusyJay/tikv