Adding some documentation to ensure methods are updated when API number is set

Bug: 32608129
Test: None (comment only change)
Change-Id: Ida34b14419e3cb86e3fe07a9cc4b7ccb46d5f5a3
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 7d5b5e6..2af953a 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -55,6 +55,10 @@
   # intermediate builds).  During development, this number remains at the
   # SDK version the branch is based on and PLATFORM_VERSION_CODENAME holds
   # the code-name of the new development work.
+
+  # When you change PLATFORM_SDK_VERSION please ensure you also update the
+  # corresponding methods for isAtLeast* in the following java file:
+  # platform/frameworks/support/compat/gingerbread/android/support/v4/os/BuildCompat.java
   PLATFORM_SDK_VERSION := 25
 endif