Doc. Update For Module Dependency Injection

Summary:
Added details about how IOS Native Modules can be initialized & registered manually with custom initializers so that dependencies can be injected to said modules.

Please let me know if there is a more appropriate place to detail this in the documentation or this is in fact detailed elsewhere; I also believe we do not have documentation on how to do the equivalent on Android, however it is a bit more obvious as the automatic MACRO registration mechanism does not exist on Android and modules need to be initialized manually anyway. As I currently understand there isn't currently any documentation detailing this apart from comments in the source.

Please let me know if you would require any style changes (variable names etc), to be more en-keeping with the rest of the documentation.
Closes facebook#8406

Differential Revision: D3843018

Pulled By: javache

fbshipit-source-id: 5f4001df32d1ddc00a9dacc4fc99b63b408f1536

docs/NativeModulesIOS.md

@@ -250,6 +250,22 @@ RCT_EXPORT_METHOD(doSomethingExpensive:(NSString *)param callback:(RCTResponseSe
 >
 > The `methodQueue` method will be called once when the module is initialized, and then retained by the bridge, so there is no need to retain the queue yourself, unless you wish to make use of it within your module. However, if you wish to share the same queue between multiple modules then you will need to ensure that you retain and return the same queue instance for each of them; merely returning a queue of the same name for each won't work.
 
+## Depedency Injection
+The bridge initializes any registered RCTBridgeModules automatically, however you may wish to instantiate your own module instances (so you may inject dependencies, for example).
+ 
+You can do this by creating a class that implements the RTCBridgeDelegate Protocol, initializing an RTCBridge with the delegate as an argument and initialising a RTCRootView with the initialized bridge.
+ 
+```objective-c
+id<RCTBridgeDelegate> moduleInitialiser = [[classThatImplementsRTCBridgeDelegate alloc] init];
+ 
+RCTBridge *bridge = [[RCTBridge alloc] initWithDelegate:moduleInitialiser launchOptions:nil];
+ 
+RCTRootView *rootView = [[RCTRootView alloc]
+                        initWithBridge:bridge
+                            moduleName:kModuleName
+                     initialProperties:nil];
+```
+
 ## Exporting Constants
 
 A native module can export constants that are immediately available to JavaScript at runtime. This is useful for communicating static data that would otherwise require a round-trip through the bridge.