Fix spacing for blimp markdown.

blimp/docs/build.md

 # Using GN
 Blimp only supports building using [GN](../../tools/gn/README.md), and only
 supports building for Android and Linux. A quick overview over how to use GN can
 be found in the GN [quick start guide](../../tools/gn/docs/quick_start.md).
 
 ## Android setup
 To setup GN, run the following command:
+
 ```
 gn args out-android/Debug
 ```
+
 This will bring up an editor, where you can type in the following:
 
 ```
 target_os = "android"
 is_debug = true
 is_clang = true
 is_component_build = true
 symbol_level = 1  # Use -g1 instead of -g2
 use_goma = true
 ```
 
 ## Linux setup
 For building for Linux, you can have a side-by-side out-directory:
+
 ```
 gn args out-linux/Debug
 ```
+
 Use the same arguments as above, but remove `target_os`.
+
 ```
 is_debug = true
 is_clang = true
 is_component_build = true
 symbol_level = 1  # Use -g1 instead of -g2
 use_goma = true
 ```
 
 # Building
 
 To build blimp, build the target ```blimp```.
 
 ## Building for Android
 
 ```
 ninja -C out-android/Debug blimp
 ```
 
 ## Building for Linux
 
 ```
 ninja -C out-linux/Debug blimp
 ```