Plugin/Proxy - update README (#1658)

* - adding policy first in the policies description

* - fix number of policies available

plugin/proxy/README.md

@@ -60,10 +60,12 @@ proxy FROM TO... {
 
 ## Policies
 
-There are three load-balancing policies available:
+There are four load-balancing policies available:
 * `random` (default) - Randomly select a backend
 * `least_conn` - Select the backend with the fewest active connections
 * `round_robin` - Select the backend in round-robin fashion
+* `first` - Select the first available backend looking by order of declaration from left to right
+
 
 All polices implement randomly spraying packets to backend hosts when *no healthy* hosts are
 available. This is to preeempt the case where the healthchecking (as a mechanism) fails.