Use GitBook for documentation (#263)

* Use gitbook for documentation

* Add section about contributing in readme of docs

.gitignore

@@ -4,3 +4,4 @@ examples/build.dev.js
 examples/build.prod.js
 node_modules
 tmp
+_book

book.json

@@ -0,0 +1,4 @@
+{
+    "root": "./docs",
+    "plugins": ["-highlight", "prism"]
+}

docs/README.md

@@ -0,0 +1,13 @@
+# Slate Documentation
+
+Slate lets you build rich, intuitive editors like those in [Medium](https://medium.com/), [Dropbox Paper](https://www.dropbox.com/paper) or [Canvas](https://usecanvas.com/)—which are becoming table stakes for applications on the web—without your codebase getting mired in complexity.
+
+It can do this because all of its logic is implemented with a series of plugins, so you aren't ever constrained by what _is_ or _isn't_ in "core". You can think of it like a pluggable implementation of `contenteditable` built on top of [React](https://facebook.github.io/react/) and [Immutable](https://facebook.github.io/immutable-js/). It was inspired by libraries like [Draft.js](https://facebook.github.io/draft-js/), [Prosemirror](http://prosemirror.net/) and [Quill](http://quilljs.com/).
+
+_**Slate is currently in beta**. It's useable now, but you might need to pull request a fix or two for advanced use cases._
+
+### Contributing!
+
+All contributions are super welcome! Check out the [Contributing instructions](https://github.com/ianstormtaylor/slate/blob/master/Contributing.md) for more info!
+
+Slate is [MIT-licensed](https://github.com/ianstormtaylor/slate/blob/master/License.md).

docs/SUMMARY.md

@@ -0,0 +1,40 @@
+# Table of Content
+
+- [Walkthroughts](./walkthroughs/README.md)
+  - [Installing Slate](./walkthroughs/installing-slate.md)
+  - [Using the Bundled Source](./walkthroughs/using-the-bundled-source.md)
+  - [Adding Event Handlers](./walkthroughs/adding-event-handlers.md)
+  - [Defining Custom Block Nodes](./walkthroughs/defining-custom-block-nodes.md)
+  - [Applying Custom Formatting](./walkthroughs/applying-custom-formatting.md)
+  - [Using Plugins](./walkthroughs/using-plugins.md)
+  - [Saving to a Database](./walkthroughs/saving-to-a-database.md)
+  - [Saving and Loading HTML Content](./walkthroughs/saving-and-loading-html-content.md)
+- [Concepts](./concepts/README.md)
+  - [Statelessness & Immutability](./concepts/statelessness-and-immutability.md)
+  - [The Document Model](./concepts/the-document-model.md)
+  - [The Selection Model](./concepts/the-selection-model.md)
+  - [Plugins](./concepts/plugins.md)
+- [Reference](./reference/README.md)
+  - Components
+    - [Editor](./reference/components/editor.md)
+    - [Placeholder](./reference/components/placeholder.md)
+  - Models
+    - [Block](./reference/models/block.md)
+    - [Character](./reference/models/character.md)
+    - [Data](./reference//models/data.md)
+    - [Document](./reference/models/document.md)
+    - [Inline](./reference/models/inline.md)
+    - [Mark](./reference//models/mark.md)
+    - [Node](./reference/models/node.md)
+    - [Selection](./reference/models/selection.md)
+    - [State](./reference/models/state.md)
+    - [Text](./reference//models/text.md)
+    - [Transform](./reference/models/transform.md)
+  - Serializers
+    - [Html](./reference/serializers/html.md)
+    - [Plain](./reference/serializers/plain.md)
+    - [Raw](./reference/serializers/raw.md)
+  - Plugins
+    - [Plugins](./reference/plugins/plugins.md)
+    - [Core](./reference/plugins/core.md)
+- [FAQ](./concepts/faq.md)