docs: weighted round robin release and architecture notes. (#562)

This accompanies https://github.com/envoyproxy/envoy/pull/2788.

Signed-off-by: Harvey Tuch <htuch@google.com>

docs/root/intro/arch_overview/load_balancing.rst

@@ -20,7 +20,12 @@ Supported load balancers
 Round robin
 ^^^^^^^^^^^
 
-This is a simple policy in which each healthy upstream host is selected in round robin order.
+This is a simple policy in which each healthy upstream host is selected in round
+robin order. If :ref:`weights
+<envoy_api_field_endpoint.LbEndpoint.load_balancing_weight>` are assigned to
+endpoints in a locality, then a weighted round robin schedule is used, where
+higher weighted endpoints will appear more often in the rotation to achieve the
+effective weighting.
 
 .. _arch_overview_load_balancing_types_least_request:
 

docs/root/intro/version_history.rst

@@ -3,6 +3,10 @@ Version history
 
 1.7.0
 =====
+* Added :ref:`weighted round robin
+  <arch_overview_load_balancing_types_round_robin>` support. The round robin
+  scheduler now respects endpoint weights and also has improved fidelity across
+  picks.
 
 1.6.0
 =====