README.md: Add note about where benchmark visualizations go
README.md: Add note about where benchmark visualizations go

alexandergall/snabbswitch,Igalia/snabb,Igalia/snabb,Igalia/snabb,eugeneia/snabb,snabbco/snabb,eugeneia/snabb,Igalia/snabbswitch,eugeneia/snabb,SnabbCo/snabbswitch,snabbco/snabb,alexandergall/snabbswitch,Igalia/snabb,snabbco/snabb,alexandergall/snabbswitch,SnabbCo/snabbswitch,snabbco/snabb,eugeneia/snabb,SnabbCo/snabbswitch,Igalia/snabb,snabbco/snabb,eugeneia/snabb,Igalia/snabbswitch,Igalia/snabb,Igalia/snabbswitch,eugeneia/snabb,snabbco/snabb,Igalia/snabbswitch,eugeneia/snabb,Igalia/snabb,alexandergall/snabbswitch,snabbco/snabb,alexandergall/snabbswitch,Igalia/snabb,alexandergall/snabbswitch,alexandergall/snabbswitch,snabbco/snabb,Igalia/snabbswitch,eugeneia/snabb,alexandergall/snabbswitch,SnabbCo/snabbswitch