Merge pull request #20087 from Tony1023/objc-readme

Added Objc readme for examples/objective-c with Bazel build

examples/objective-c/helloworld/README.md

@@ -1,12 +1,18 @@
 # gRPC in 3 minutes (Objective-C)
 
+There are currently two ways to build projects with the gRPC Objective-C library:
+* Cocoapods & Xcode
+* Bazel (experimental)
+
+## Cocoapods
+
 ## Installation
 
 To run this example you should have [Cocoapods](https://cocoapods.org/#install) installed, as well
 as the relevant tools to generate the client library code (and a server in another language, for
 testing). You can obtain the latter by following [these setup instructions](https://github.com/grpc/homebrew-grpc).
 
-## Hello Objective-C gRPC!
+### Hello Objective-C gRPC!
 
 Here's how to build and run the Objective-C implementation of the [Hello World](../../protos/helloworld.proto)
 example used in [Getting started](https://github.com/grpc/grpc/tree/master/examples).
@@ -27,7 +33,7 @@ Change your current directory to `examples/objective-c/helloworld`
 $ cd examples/objective-c/helloworld
 ```
 
-### Try it!
+#### Try it!
 To try the sample app, we need a gRPC server running locally. Let's compile and run, for example,
 the C++ server in this repository:
 
@@ -53,6 +59,49 @@ code in `main.m` and see the results in XCode's log console.
 The code sends a `HLWHelloRequest` containing the string "Objective-C" to a local server. The server
 responds with a `HLWHelloResponse`, which contains a string that is then output to the log.
 
+## Bazel
+### Installation
+To run the examples in Bazel, you should have [Bazel](https://docs.bazel.build/versions/master/install-os-x.html) installed.
+
+### Hello Objective-C gRPC!
+Here's how to build and run the Objective-C implementation of the [Hello World](helloworld) example.
+
+The code for the Hello World example and others live in the `examples` directory. Clone this repository to your local machine by running the following commands:
+```shell
+$ git clone --recursive https://github.com/grpc/grpc
+```
+
+Next, change your directory to `examples/objective-c`
+```shell
+$ cd grpc/examples/objective-c
+```
+
+Now build the Hello World project:
+```shell
+$ bazel build :HelloWorld
+```
+
+#### Try it!
+To run the Hello World sample properly, we need a local server. Let's compile and run the corresponding C++ server:
+```shell
+$ bazel run //examples:greeter_server
+```
+
+To run the sample, you need to know the available simulator runtimes in your machine. You could either list the available runtimes yourself by running:
+```shell
+$ xcrun simctl list
+```
+Or just try running the app and it will let you know what is available in the error messages:
+```shell
+$ bazel run :HelloWorld
+```
+Note that running this command will build the project even if it is not built beforehand.
+
+Finally, launch the app with one of the available runtimes:
+```shell
+$ bazel run :HelloWorld --ios_simulator_version='<runtime>' --ios_sumlator_device='<device>'
+```
+
 ## Tutorial
 
 You can find a more detailed tutorial in [gRPC Basics: Objective-C](https://grpc.io/docs/tutorials/basic/objective-c.html).