add: discovery overview

content/concepts/discovery/overview.md

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+---
+title: "What is Peer Discovery"
+description: "Peer discovery protocols are used to discover and announce services to other peers."
+weight: 221
+---
+
+## Overview
+
+Distributed networks require a way to discover peers. Peer discovery in distributed networks
+is the process of using a discovery protocol to discover and announce services to other
+available peers. Peer discovery requires each node in a network to be able to discover other
+nodes without the need for a central server.
+
+## Peer discovery in libp2p
+
+Peers can discover other peers in libp2p using a variety of mechanisms, such as
+exchanging peer addresses over the network, querying a directory service, or using a
+[DHT (distributed hash table)](../fundamentals/dht) to store and retrieve information about
+available peers. The process of peer discovery varies on the composition of protocols being
+used to connect peers.
+
+Generally, peer discovery is a function in respect to a topic that returns a list of
+peers, usually their multiaddr and port information.
+
+The methods for peer discovery in libp2p are, but are not limited to:
+
+- [rendezvous](rendezvous);
+- [mDNS](mdns);
+- [publish/subscribe](../pubsub/overview.md)
+- and using a [DHT](../../concepts/introduction/protocols/dht.md).