Remove gists and fix iOS instructions

Summary:
Remove gists in code blocks. This also made it easier to fix the iOS sample app instructions in the getting started.

>Note: I also needed to update my gems as I was having problems running `bundle install`. The errors were around installing json v1.8.3. It was resolved by creating a new Gemfile.lock.

1. Build website and check changed pages (see attached Getting Started for an example)
2. Also check how it would look for mobile site (see attached index page)

Verified that the code snippets matched previous snippets and styling acceptable.

![yoga_gs](https://cloud.githubusercontent.com/assets/691109/24681238/1601fcc8-1949-11e7-8caa-5ac78a4c9a6b.png)
![yoga_index_mobile](https://cloud.githubusercontent.com/assets/691109/24681248/1ee3ea86-1949-11e7-9677-83056f93e385.png)
Closes https://github.com/facebook/yoga/pull/500

Differential Revision: D4834356

Pulled By: emilsjolander

fbshipit-source-id: f47dca4b7518822b195f0bd5076fbf852904372b

docs/_docs/getting-started.md

@@ -19,13 +19,22 @@ For now we recommend including Yoga as a [git submodule](https://git-scm.com/doc
 
 Yoga ships with an [iOS example](https://github.com/facebook/yoga/tree/master/YogaKit/YogaKitSample). To get it running:
 
-<script src="https://gist.github.com/emilsjolander/903b16185b24c957acc4cd250c6e73d9.js"></script>
+```sh
+$ git clone https://github.com/facebook/yoga.git
+$ cd open yoga/YogaKit/YogaKitSample/
+$ pod install
+$ open YogaKitSample.xcworkspace
+```
 
 #### Android
 
 Yoga ships with an [Android example too](https://github.com/facebook/yoga/tree/master/android/sample). To get it running on an attached device (or emulator):
 
-<script src="https://gist.github.com/rspencer01/a512f7cd24055c948675be15d48eba78.js"></script>
+```sh
+$ git clone https://github.com/facebook/yoga.git
+$ cd yoga
+$ buck install -r android/sample
+```
 
 Actually, this is more than just an example, and more a layout system for Android using Yoga in general (see `YogaLayout`).  For more information see the [Android API section](/yoga/docs/api/android).
 
@@ -35,4 +44,15 @@ Yoga uses [Buck](https://buckbuild.com/) as its build system. Buck is not requir
 
 If you are using Buck all you need to do is reference the language bindings you want to use in your `BUCK` file.
 
-<script src="https://gist.github.com/emilsjolander/895b4ec79425882b8d4676b6545d6943.js"></script>
+```sh
+deps = [
+  # C
+  '//path/to/submodule/yoga:yoga',
+  
+  # Java
+  '//path/to/submodule/yoga/java:jni',
+  
+  # Objective-C
+  '//path/to/submodule/yoga/YogaKit:YogaKit',
+]
+```