Review comments.

Author: stevesg

cortex-mixin/docs/playbooks.md

@@ -576,7 +576,7 @@ This alert fires when any instance does not register all other instances as memb
 
 How it **works**:
 - This alert applies when memberlist is used for the ring backing store.
-- All Cortex instances, regardless of type, join the a single memberlist cluster.
+- All Cortex instances using the ring, regardless of type, join a single memberlist cluster.
 - Each instance (=memberlist cluster member) should be able to see all others.
 - Therefore the following should be equal for every instance:
   - The reported number of cluster members (`memberlist_client_cluster_members_count`)
@@ -587,7 +587,7 @@ How to **investigate**:
 - If the count is zero:
   - It is possible that the joining the cluster has yet to succeed.
   - The following log message indicates that the _initial_ initial join did not succeed: `failed to join memberlist cluster`
-  - The following log messages indicate that subsequent re-join attempts are failing: `re-joining memberlist cluster failed`
+  - The following log message indicates that subsequent re-join attempts are failing: `re-joining memberlist cluster failed`
   - If it is the case that the initial join failed, take action according to the reason given.
 - Verify communication with other members by checking memberlist traffic is being sent and received by the instance using the following metrics:
   - `memberlist_tcp_transport_packets_received_total`