-Add README for building go sample application

mojo/go/sample_app/README.txt

 Sample Go application that can be loaded into a mojo shell running on Android.
 The application exports a MojoMain entry point for the shell and then makes
 a GetTimeTicksNow system call.
 
-Build instructions
-gn args <output_directory>
+Setup instructions
+
+1) Download/Install the NDK toolchain from 
+http://developer.android.com/tools/sdk/ndk/index.html
+
+$ NDK_ROOT=$HOME/android/ndk-toolchain
+$ ./build/tools/make-standalone-toolchain.sh --platform=android-9 --install-dir=$NDK_ROOT
+$ NDK_CC=$NDK_ROOT/bin/arm-linux-androideabi-gcc

[qsr, 2014/10/30 10:43:47]

Why do you need all of this? If you have an android checkout, this is already in
third-party. Am I missing something?

[gauthamt, 2014/10/30 17:51:22]

Modified the instructions to just generate the desired toolchain from
third-party. 

I saw that some of the pre-built toolchains dont seem to have all the libraries
(eg: sysroot/,  include/)

+
+2) Download/Install the Go compiler
+
+$ unset GOBIN GOPATH GOROOT
+$ hg clone https://code.google.com/p/go
+$ cd go/src
+$ CC_FOR_TARGET=$NDK_CC GOOS=android GOARCH=arm GOARM=7 ./make.bash
+$ ls ../bin/go
+
+3) Now, we switch to the Mojo workspace and build the sample application.
+
+$ cd mojo/src
+$ gn args <output_directory>
 
 Set the following arguments
 mojo_use_go=true
-go_build_tool=<go_binary_location>
+go_build_tool="<path_to_go_binary>"
 os="android"
 
-gn gen <output_directory>
-ninja -C <output_directory> go_sample_app
-
-You can now following instructions from the below link to run the app.
-http://dev.chromium.org/developers/how-tos/run-mojo-shell
-
-Start the Go application.
-./build/android/adb_run_mojo_shell http://127.0.0.1:4444/go_sample_app
+$ gn gen <output_directory>
+$ ninja -C <output_directory> go_sample_app