rewrite build instructions (#1178)
rewrite build instructions (#1178)

* rewrite build instructions

make them short
too much information
replace descriptions by links to the istio/istio development document

* added minimal bazel version

* removed mentioning vagrant

* make build instructions as short as possible

reference the main Istio Development guide
state the differences in pilot

mandarjog/istio,sebastienvas/istio,istio/istio,istio/istio,sebastienvas/istio,mandarjog/istio,smawson/istio,frankbu/istio,geeknoid/istio,smawson/istio,geeknoid/istio,frankbu/istio,istio/istio,smawson/istio,mandarjog/istio,istio/istio,geeknoid/istio,geeknoid/istio,sebastienvas/istio,mandarjog/istio,sebastienvas/istio,istio/istio,frankbu/istio,sebastienvas/istio,smawson/istio,frankbu/istio,frankbu/istio,smawson/istio,mandarjog/istio,geeknoid/istio,smawson/istio,frankbu/istio,geeknoid/istio