README.md in snapshot-0.5.0 vs README.md in snapshot-0.6.0

@@ -231,22 +231,23 @@
 ios_version "9.0"
 ```
 
 ### Custom Args for the build command
 Use the ```custom_args``` directive to prepend custom statements to the build command.
-```ruby
-custom_args "GCC_PREPROCESSOR_DEFINITIONS='SCREENSHOTS'"
-```
+
 Add a ```custom_build_args``` line to your ```Snapfile``` to add custom arguments to the build command.
+
+Here is an example for adding a preprocessor macro `SNAPSHOT` and  a custom build setting `SNAPSHOT_ENABLE`.
+
 ```ruby
-custom_build_args "-configuration release"
+custom_build_args "GCC_PREPROCESSOR_DEFINITIONS='$(inherited) SNAPSHOT=1' SNAPSHOT_ENABLE = YES"
 ```
 
 ### Custom Build Command
 If for some reason, the default build command does not work for your project, you can pass your own build script. The script will be executed **once** before the tests are being run.
 
-**Make sure** you are setting the output path to ```/tmp/snapshot```.
+**Make sure** you are setting the output path to ```/tmp/snapshot``` or specify a custom ```build_dir``` on your ```Snapfile```.
 
 ```ruby
 build_command "xcodebuild DSTROOT='/tmp/snapshot' OBJROOT='/tmp/snapshot' SYMROOT='/tmp/snapshot' ... "
 ```
 
@@ -346,9 +347,36 @@
 
 ## Instruments is not responding
 Unfortunately ```Instruments``` sometimes decides, to not respond to anything. Which means, neither the ```Instruments``` application, nor the ```instruments``` command line work. Killing the process doesn't help.
 
 The only way to fix this, is a restart of the Mac. 
+
+## Use a custom build system
+Using a build systems not based on Xcode –such as RubyMotion or Xamarin– is also possible.
+
+### RubyMotion
+
+Add to your ```Snapfile```:
+
+```ruby
+build_dir 'build/iPhoneSimulator-7.0-Development'
+build_command 'rake build:simulator'
+```
+
+### Xamarin
+
+Add to your ```Snapfile```:
+
+```ruby
+build_dir 'YourProject/bin/iPhoneSimulator'
+build_command '/Applications/Xamarin\ Studio.app/Contents/MacOS/mdtool -v build "--configuration:Debug|iPhoneSimulator" YourProject.sln'
+```
+
+Unfortunately, Xamarin command line tool is only available for Business Edition licenses. For Indie licenses you can build the app using Xamarin Studio and use the ```--nobuild``` option.
+
+### Skip building
+
+If building via command-line doesn't work for your project or you don't want to build every time, you can run the tool with ```snapshot --nobuild``` to skip the build process and use a pre-built ```.app``` under your ```build_dir```.
 
 # Need help?
 - If there is a technical problem with ```snapshot```, submit an issue.
 - I'm available for contract work - drop me an email: [e-mail]