Update build notes to include ref. to android-7 platform requirement

Author: developernotes

README.org

@@ -55,7 +55,7 @@ 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.  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.  To complete the =make init= command, you will need the =android-7= platform installed from the SDK.  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