Update 06-overlay-networks.md

Author: Mano Marks

networking/concepts/06-overlay-networks.md

@@ -24,7 +24,7 @@ In this diagram we see the packet flow on an overlay network. Here are the steps
 
 
 
-###Overlay Driver Internal Architecture
+### Overlay Driver Internal Architecture
 The Docker Swarm control plane automates all of the provisioning for an overlay network. No VXLAN configuration or Linux networking configuration is required. Data-plane encryption, an optional feature of overlays, is also automatically configured by the overlay driver as networks are created. The user or network operator only has to define the network (`docker network create -d overlay ...`) and attach containers to that network.
 
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