Add COCOAPODS.md with installation instructions (#58)

Author: liamnichols

COCOAPODS.md

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+# CocoaPods
+
+## Basic Integration
+
+To integrate TIP into your iOS project using CocoaPods, simply add the following to your **Podfile**:
+
+```ruby
+target 'MyApp' do
+  pod 'TwitterImagePipeline', '~> 2.24.1'
+end
+```
+
+Then run a `pod install` inside your terminal, or from CocoaPods.app.
+
+## Extended Integration
+
+TIP also has support for two additional codecs that are not included with the default installation:
+
+- WebP (Backwards compatible to iOS 10)
+- MP4
+
+If you wish to include these codecs, modify your **Podfile** to define the appropriate subspecs like the examples below:
+
+```ruby
+target 'MyApp' do
+  pod 'TwitterImagePipeline', '~> 2.24.1', :subspecs => ['WebPCodec/Default']
+
+  pod 'TwitterImagePipeline', '~> 2.24.1', :subspecs => ['WebPCodec/Animated']
+
+  pod 'TwitterImagePipeline', '~> 2.24.1', :subspecs => ['MP4Codec']
+
+  pod 'TwitterImagePipeline', '~> 2.24.1', :subspecs => ['WebPCodec/Animated', 'MP4']
+end
+```
+
+- **`WebP/Default`**: Includes the `TIPXWebPCodec` with the WebP framework for basic WebP support.
+- **`WebP/Animated`**: Adds additional support to the `TIPXWebPCodec` for demuxing WebP data allowing for animated images.
+- **`MP4Codec`**: Includes the `TIPXMP4Codec`.
+
+**Note:** You are still required to add these codecs to the `TIPImageCodecCatalogue` manually:
+
+```objc
+- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
+{
+    TIPImageCodecCatalogue *codecCatalogue = [TIPImageCodecCatalogue sharedInstance];
+
+    [codecCatalogue setCodec:[[TIPXWebPCodec alloc] initPreservingDefaultCodecsIfPresent:NO]
+                forImageType:TIPImageTypeWEBP];
+
+    [codecCatalogue setCodec:[[TIPMP4Codec alloc] init]
+                forImageType:TIPXImageTypeMP4];
+
+    // ...
+}
+```