Fix the VSL Proxy tag documentation
Fix the VSL Proxy tag documentation

Both contents and formatting were off.

gquintard/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,varnish/Varnish-Cache,varnish/Varnish-Cache,varnish/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache,varnish/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache,varnish/Varnish-Cache