Update README.md

Adding some changes and notes for compiling on windows.

Author: moritz-wundke

README.md

@@ -29,12 +29,17 @@ To compile Boost for Android you may use one of the following NDKs:
 
 ### Compiling
 
-    Linux:
-    $ ./build-android.sh $(NDK_ROOT)
- 
-    Windows:
-    > build-android.bat $(NDK_ROOT)
-    NOTE: Do not forget to replace backslash with slashes in $(NDK_ROOT). For example set $(NDK_ROOT) to D:/android-ndk-r8e instead of D:\android-ndk-r8e
+Linux.
+```
+./build-android.sh $(NDK_ROOT)
+```
+Windows:
+```
+build-android.bat $(NDK_ROOT)
+```
+NOTE: Do not forget to replace backslash with slashes in $(NDK_ROOT). For example set $(NDK_ROOT) to D:/android-ndk-r8e instead of D:\android-ndk-r8e
+    
+On windows you will need MSYS to be able to launch the corresponding bat files (http://www.mingw.org/wiki/MSYS).
 
 This command will download and build boost against the NDK specified and output the final headers and libs in the `build` folder. Make sure to provide an absolute path the the NDK folder!