Update README to document the need for defining ANDROID_NDK_ROOT

Author: developernotes

README.org

@@ -59,7 +59,7 @@ Notepadbot is a sample application pulled from the standard Android samples code
 
 *** Building
 
-In order to build android-database-sqlcipher from source you will need both the Android SDK as well as Android NDK.  We currently recommend using Android NDK version r11c.  To complete the =make init= command, you will need the =android-19= platform installed from the SDK.  Once you have cloned the repo, change directory into the root of the repository and run the following commands:
+In order to build android-database-sqlcipher from source you will need both the Android SDK as well as Android NDK.  We currently recommend using Android NDK version r11c.  To complete the =make init= command, you will need the =android-19= platform installed from the SDK.  The =make init= command will build OpenSSL for the required platforms, thus the =ANDROID_NDK_ROOT= environment variable must be defined which should point to your NDK root. Once you have cloned the repo, change directory into the root of the repository and run the following commands:
 
 :  # this only needs to be done once
 :  make init