Adding in some documentation to ensure files are updated as needed

Also pulls forward the comments added in 9a3d92f71981bfd06816d2cb331f41e783761c43
to nyc-mr2-dev

Bug: 33090697
Bug: 32608129
Test: None (comment only change)
Change-Id: Ic23d099767ad4c711bf2d3586cdefd626dec1ce0
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 0258bf7..8557e72 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -43,6 +43,15 @@
   # which is the version that we reveal to the end user.
   # Update this value when the platform version changes (rather
   # than overriding it somewhere else).  Can be an arbitrary string.
+
+  # When you add a new PLATFORM_VERSION which will result in a new
+  # PLATFORM_SDK_VERSION please ensure you add a corresponding isAtLeast*
+  # method in the following java file:
+  # frameworks/support/compat/gingerbread/android/support/v4/os/BuildCompat.java
+
+  # When you change PLATFORM_VERSION for a given PLATFORM_SDK_VERSION
+  # please add that PLATFORM_VERSION to the following text file:
+  # cts/tests/tests/os/assets/platform_versions.txt
   PLATFORM_VERSION := 7.1.2
 endif
 
@@ -55,6 +64,14 @@
   # 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:
+  # frameworks/support/compat/gingerbread/android/support/v4/os/BuildCompat.java
+
+  # When you increment the PLATFORM_SDK_VERSION please ensure you also
+  # clear out the following text file of all older PLATFORM_VERSION's:
+  # cts/tests/tests/os/assets/platform_versions.txt
   PLATFORM_SDK_VERSION := 25
 endif