move mongodb and firebase deps to devDependencies

docs/multiplayer.md

@@ -194,11 +194,13 @@ $ npx babel-node --presets zero src/server.js
 Navigate to http://localhost:8000/
 ```
 
-#### Database
+#### Storage
 
-The default storage implementation is an in-memory map. However,
-you can provide your own adapter to connect to any backend, or
-use the bundled MongoDB connector.
+The default storage implementation is an in-memory map.
+If you want something that's more persistent, you can use one
+of the bundled connectors for various backends, or even implement
+your own connector. For example, here is how you can keep your
+game state in a MongoDB.
 
 ```js
 const { Server, Mongo } = require('boardgame.io/server');
@@ -215,4 +217,4 @@ const server = Server({
 server.run(8000);
 ```
 
-!> You can get a free MongoDB instance at places like mlab.com.
+See [here](storage.md) for more details about how to customize storage.

docs/storage.md

@@ -0,0 +1,63 @@
+# Storage
+
+The framework comes bundled with various connectors to different backends
+depending on how you want to persist your game state.
+
+### MongoDB
+
+First, install the `mongodb` package:
+
+```
+npm install --save mongodb
+```
+
+Then modify your server spec to indicate that you want to connect to Mongo:
+
+```js
+const { Server, Mongo } = require('boardgame.io/server');
+const { TicTacToe } = require('./game');
+
+const server = Server({
+  games: [TicTacToe],
+
+  db: new Mongo({
+    url: 'mongodb://...',
+    dbname: 'bgio',
+  }),
+});
+
+server.run(8000);
+```
+
+!> You can get a free Mongo instance at places like [mLab](https://mlab.com/).
+
+### Firebase
+
+First, install the necessary packages:
+
+```
+npm install --save firebase
+```
+
+Then modify your server spec to indicate that you want to connect to Firebase:
+
+```js
+const { Server, Firebase } = require('boardgame.io/server');
+const { TicTacToe } = require('./game');
+
+const server = Server({
+  games: [TicTacToe],
+
+  db: new Firebase({
+    config: {
+      apiKey: '...',
+      authDomain: '...',
+      databaseURL: '...',
+      projectID: '...',
+    },
+    dbname: 'bgio',
+  }),
+});
+
+server.run(8000);
+```