docs: update mdns example and docs (#3056)

* docs: update mdns example and docs

* docs: add link to specs

---------

Co-authored-by: Daniel N <[email protected]>
Co-authored-by: Chad Nehemiah <[email protected]>

Author: 2color

doc/CONFIGURATION.md

@@ -127,17 +127,13 @@ If you want to know more about libp2p connection encryption, you should read the
 
 Some available peer discovery modules are:
 
-- [@libp2p/mdns](https://github.com/libp2p/js-libp2p/tree/main/packages/peer-discovery-mdns)
-- [@libp2p/bootstrap](https://github.com/libp2p/js-libp2p/tree/main/packages/peer-discovery-bootstrap)
-- [@libp2p/kad-dht](https://github.com/libp2p/js-libp2p/tree/main/packages/kad-dht)
-- [@chainsafe/discv5](https://github.com/chainsafe/discv5)
+- [@libp2p/mdns](https://github.com/libp2p/js-libp2p/tree/main/packages/peer-discovery-mdns) ([spec](https://github.com/libp2p/specs/blob/master/discovery/mdns.md))
+- [@libp2p/kad-dht](https://github.com/libp2p/js-libp2p/tree/main/packages/kad-dht) ([spec](https://github.com/libp2p/specs/blob/master/kad-dht/README.md))
+- [@libp2p/bootstrap](https://github.com/libp2p/js-libp2p/tree/main/packages/peer-discovery-bootstrap) (typically used together with @libp2p/kad-dht)
+- [@chainsafe/discv5](https://github.com/chainsafe/discv5) ([spec](https://github.com/ethereum/devp2p/blob/master/discv5/discv5.md))
 
 If none of the available peer discovery protocols fulfills your needs, you can create a libp2p compatible one. A libp2p peer discovery protocol just needs to be compliant with the [Peer Discovery Interface](https://github.com/libp2p/js-libp2p/tree/main/packages/interface/src/peer-discovery).
 
-If you want to know more about libp2p peer discovery, you should read the following content:
-
-- https://github.com/libp2p/specs/blob/master/discovery/mdns.md
-
 ### Content Routing
 
 > Content routing provides a way to find where content lives in the network. It works in two steps: 1) Peers provide (announce) to the network that they are holders of specific content and 2) Peers issue queries to find where that content lives. A Content Routing mechanism could be as complex as a DHT or as simple as a registry somewhere in the network.
@@ -268,7 +264,7 @@ const node = await createLibp2p({
   ],
   streamMuxers: [yamux()],
   connectionEncrypters: [noise()],
-  peerDiscovery: [MulticastDNS],
+  peerDiscovery: [mdns()],
   services: {
     dht: kadDHT(),
     pubsub: gossipsub()
@@ -303,8 +299,17 @@ const node = await createLibp2p({
     })
   ]
 })
+
+node.addEventListener('peer:discovery', (event) => {
+  console.log('Discovered new peer:', event.detail.id.toString())
+  node.dial(event.detail.multiaddrs)
+})
 ```
 
+Note the `bootstrap` peer discovery module will automatically dial the bootstrap peers when the node starts up, while `mdns` will only trigger the `peer:discovery` event when a new peer is discovered.
+
+
+
 #### Customizing Pubsub
 
 Before a peer can subscribe to a topic it must find other peers and establish network connections with them. The pub/sub system doesn’t have any way to discover peers by itself. Instead, it relies upon the application to find new peers on its behalf, a process called ambient peer discovery.

packages/peer-discovery-mdns/README.md

@@ -39,6 +39,7 @@ const libp2p = await createLibp2p({
 })
 
 libp2p.addEventListener('peer:discovery', (evt) => {
+  libp2p.dial(evt.detail.multiaddrs) // dial discovered peers
   console.log('found peer: ', evt.detail.toString())
 })
 ```

packages/peer-discovery-mdns/src/index.ts

@@ -16,6 +16,7 @@
  * })
  *
  * libp2p.addEventListener('peer:discovery', (evt) => {
+ *   libp2p.dial(evt.detail.multiaddrs) // dial discovered peers
  *   console.log('found peer: ', evt.detail.toString())
  * })
  * ```