Add a description how to install android-ndk r10d.
Add a description how to install android-ndk r10d.

Closes #1576

horie1024/realm-java,teddywest32/realm-java,teddywest32/realm-java,ShikaSD/realm-java,ShikaSD/realm-java,realm/realm-java,realm/realm-java,ShikaSD/realm-java,horie1024/realm-java,realm/realm-java,realm/realm-java,horie1024/realm-java,realm/realm-java,teddywest32/realm-java,realm/realm-java,ShikaSD/realm-java,teddywest32/realm-java,realm/realm-java,teddywest32/realm-java,ShikaSD/realm-java