README: improve installation instructions
README: improve installation instructions

rlane/ivs,vezril/ivs,floodlight/ivs,rlane/ivs,floodlight/ivs,vezril/ivs,harshsin/ivs,rlane/ivs,rlane/ivs,harshsin/ivs,floodlight/ivs,harshsin/ivs,harshsin/ivs,vezril/ivs