refactor: peristent peer-store extended class and disabled by defaul

doc/API.md

@@ -74,6 +74,7 @@ Creates an instance of Libp2p.
 | [options.dialer] | `object` | libp2p Dialer configuration
 | [options.metrics] | `object` | libp2p Metrics configuration
 | [options.peerId] | [`PeerId`][peer-id] | peerId instance (it will be created if not provided) |
+| [options.peerStore] | [`PeerId`][peer-id] | libp2p PeerStore configuration |
 
 For Libp2p configurations and modules details read the [Configuration Document](./CONFIGURATION.md).
 

doc/CONFIGURATION.md

@@ -506,6 +506,32 @@ const node = await Libp2p.create({
 })
 ```
 
+#### Configuring PeerStore
+
+PeerStore persistence is disabled in libp2p by default. You can enable and configure it as follows. Aside from enabled being `false` by default, it will need an implementation of a [datastore](https://github.com/ipfs/interface-datastore).
+
+```js
+const Libp2p = require('libp2p')
+const TCP = require('libp2p-tcp')
+const MPLEX = require('libp2p-mplex')
+const SECIO = require('libp2p-secio')
+
+const LevelStore = require('datastore-level')
+
+const node = await Libp2p.create({
+  modules: {
+    transport: [TCP],
+    streamMuxer: [MPLEX],
+    connEncryption: [SECIO]
+  },
+  datastore: new LevelStore('path/to/store'),
+  peerStore: {
+    persistence: true,
+    threshold: 5
+  }
+})
+```
+
 #### Customizing Transports
 
 Some Transports can be passed additional options when they are created. For example, `libp2p-webrtc-star` accepts an optional, custom `wrtc` implementation. In addition to libp2p passing itself and an `Upgrader` to handle connection upgrading, libp2p will also pass the options, if they are provided, from `config.transport`.