Tweak README a little bit
Tweak README a little bit

This changes the markdown style in README to match that used everywhere
else in the branch.

It also adds a reference to the bug tracker and CONTRIBUTING.md.

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

benaryorg/lxd,jensg-st/lxd,benaryorg/lxd,erikmack/lxd,mjeanson/lxd,akshaykarle/lxd,dustinkirkland/lxd,beni55/lxd,Skarlso/lxd,jsavikko/lxd,georghopp/lxd,rcj4747/lxd,dvbportal/osx-lxd,mikemccracken/lxd,Malizor/lxd,mikemccracken/lxd,yura-pakhuchiy/lxd,ollie314/lxd,dvbportal/osx-lxd,lxc/lxd,tych0/lxd,jensg-st/lxd,ollie314/lxd,jumpstarter-io/lxd,ollie314/lxd,jsavikko/lxd,stgraber/lxd,rrva/lxd,Skarlso/lxd,techtonik/lxd,lxc/lxd,basvanbeek/lxd,smoser/lxd,mjeanson/lxd,georghopp/lxd,sl1pm4t/lxd,mjeanson/lxd,lxc/lxd,basvanbeek/lxd,lxc/lxd,stgraber/lxd,smoser/lxd,akshaykarle/lxd,yura-pakhuchiy/lxd,stgraber/lxd,stgraber/lxd,ericsnowcurrently/lxd,rcj4747/lxd,dustinkirkland/lxd,chrisglass/lxd,rrva/lxd,lxc/lxd,erikmack/lxd,hallyn/lxd,erikmack/lxd,tych0/lxd,sl1pm4t/lxd,sl1pm4t/lxd,Malizor/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,Malizor/lxd,chrisglass/lxd,stgraber/lxd,benaryorg/lxd,ericsnowcurrently/lxd,stgraber/lxd,stgraber/lxd,rrva/lxd,akshaykarle/lxd,jensg-st/lxd,Skarlso/lxd,georghopp/lxd,tych0/lxd,atxwebs/lxd,jsavikko/lxd,pcdummy/lxd,techtonik/lxd,hallyn/lxd,achanda/lxd,rcj4747/lxd,dvbportal/osx-lxd,mikemccracken/lxd,atxwebs/lxd,atxwebs/lxd,basvanbeek/lxd,jumpstarter-io/lxd,atxwebs/lxd,yura-pakhuchiy/lxd,techtonik/lxd,lxc/lxd,pcdummy/lxd,hallyn/lxd,beni55/lxd,hallyn/lxd,chrisglass/lxd,ericsnowcurrently/lxd,achanda/lxd,achanda/lxd,beni55/lxd,dustinkirkland/lxd,jumpstarter-io/lxd,smoser/lxd,Skarlso/lxd,pcdummy/lxd