Add docs, correct URL

docs/infrastructure/message_queue.md

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+---
+title: Message Queue
+layout: default
+nav_order: 1
+parent: Infrastructure
+---
+
+The Message Queue is a microservice to authenticate and relay messages between
+services. It offers just three functions:
+
+1) Queue a message.
+2) Receive the next message.
+3) Acknowledge a message, removing it from the queue.
+
+This ensures messages are delivered between services, with their order
+preserved. This also ensures that if a service reboots while handling a message,
+it'll still handle the message once rebooted (and the message will not be lost).
+
+The Message Queue also aims to offer increased liveliness and performance.
+If services directly communicated, the rate at which one service could operate
+would always be bottlenecked by the service it communicates with. If the
+receiving service ever went offline, the sending service wouldn't be able to
+deliver messages until the receiver came back online, halting its own work. By
+defining a dedicated microservice, with a lack of complex logic, it's much less
+likely to go offline or suffer from degraded performance.