[objc][docs] Add iOS getting started docs. (#266)

* [objc][docs] Add iOS getting started docs.

* [objc] Fix a few grammar issues.

docs/getting-started-objc-ios.md

@@ -0,0 +1,92 @@
+# Getting started with iOS
+
+This is the getting started page for iOS.
+
+*Working for tvOS or watchOS is very similar to iOS. You should start with the iOS instructions and then apply them to your platform of choice.*
+
+## Requirements
+
+In order to use the embeddinator to generate bindings for iOS you'll need a Mac running:
+
+* macOS 10.12 (Sierra) or later
+* Xcode 8.3.2 or later
+* [Mono 5.0](http://www.mono-project.com/download/beta/) _presently in beta_ or later
+* [Xamarin.iOS](https://jenkins.mono-project.com/view/Xamarin.MaciOS/job/xamarin-macios-builds-master/) from our _master_ branch.
+
+Optionally you can install [Xamarin Studio](https://developer.xamarin.com/guides/cross-platform/xamarin-studio/)
+or the new [Visual Studio for Mac](https://www.visualstudio.com/vs/visual-studio-mac/)
+to edit and compile your C# code. The rest of the getting started
+guide assume you'll be using **Visual Studio for Mac**.
+
+Notes:
+
+* Earlier versions of macOS, Xcode and Mono _might_ work, but are untested and unsupported;
+* Code generation can be done on Windows, but it is only possible to compile it on a Mac computer where Xcode is installed;
+
+## Hello world
+
+First let's build a simple hello world example in C#.
+
+### Create C# sample
+
+Open Visual Studio for Mac, create a new iOS Class Library project, name it `hello-from-csharp`, and save it to `~/Projects/hello-from-csharp`.
+
+Replace the code in the `MyClass.cs` file with the following snippet:
+
+```csharp
+using UIKit;
+public class MyUIView : UITextView
+{
+	public MyUIView ()
+	{
+		Text = "Hello from C#";
+	}
+}
+```
+
+Build the project, the resulting assembly will be saved as `~/Projects/hello-from-csharp/hello-from-csharp/bin/Debug/hello-from-csharp.dll`.
+
+### Bind the managed assembly
+
+Run the embeddinator to create a native framework for the managed assembly:
+
+```shell
+cd ~/Projects/hello-from-csharp
+/Library/Frameworks/Xamarin.Embeddinator-4000/Commands/objcgen ~/Projects/hello-from-csharp/hello-from-csharp/bin/Debug/hello-from-csharp.dll --target=framework --platform=iOS --outdir=output -c --debug
+```
+
+The framework will be placed in `~/Projects/hello-from-csharp/output/hello-from-csharp.framework`.
+
+### Use the generated output in an Xcode project
+
+Open Xcode and create a new iOS Single View Application, name it `hello-from-csharp`.
+
+Open the `~/Projects/hello-from-csharp/output` directory in Finder, select `hello-from-csharp.framework`, drag it to the Xcode project and drop it just above the `hello-from-csharp` folder in the project.
+
+Make sure `Copy items if needed` is checked in the dialog that pops up, and click `Finish`.
+
+In the project's General tab, add `hello-from-csharp.framework` as an Embedded Binary.
+
+Open ViewController.m, and replace the contents with:
+
+```objective-c
+#import "ViewController.h"
+#include "hello-from-csharp/hello-from-csharp.h"
+
+@interface ViewController ()
+@end
+
+@implementation ViewController
+- (void)viewDidLoad {
+    [super viewDidLoad];
+
+    MyUIView *view = [[MyUIView alloc] init];
+    view.frame = CGRectMake(0, 200, 200, 200);
+    [self.view addSubview: view];
+}
+@end
+```
+
+Finally run the Xcode project, and something like this will show up:
+
+![Hello from C# sample running in the simulator](hello-from-csharp-ios.png)